Potential underfloor heating problems and how to solve them

Like any heating system, there may be times when the underfloor heating (UFH) doesn’t seem to be working as it should. Nu-Heat’s Technical Team helps you to find the root of the problem, whether electrical or down to a failed part, to get the system up and running again.

Let’s take a look at a few of the potential problems you may come across with UFH and how to go about solving them.

UFH system

Underfloor heating single zone not heating up

If a single zone is not heating up as expected, it could be caused by a number of small problems that are all fairly simple to resolve:

  • A sticky pin valve underneath an actuator
    There is a small pin underneath each actuator. You need to remove the actuator from the affected zone to check that the pin valve is free. If it’s stuck down it can be freed using a silicone spray. You can also use a pair of long nose pliers to try and free the pin.
  • Actuator failed
    If an actuator has failed, this is most likely due to an electrical issue that could relate to a thermostat or wiring board. It’s best to consult a qualified electrician to check the circuits.
    A faulty actuator can also cause the UFH to be permanently switched on.
  • Faulty thermostat
    You can easily reset a thermostat by following the user guide. If the system uses wireless, battery-powered thermostats then it’s also a good idea to check the batteries. If neither of these options works, it could potentially be an electrical fault so a qualified electrician should be called.
    A faulty thermostat can also cause the UFH to be permanently switched on.

  • Air in UFH loop
    There could be some air trapped in the UFH pipework. In order to remove the air you will need to:

    1. Isolate all of the UFH zones except for the zone that is not heating up
    2. Remove the actuator
    3. Connect a hosepipe to the flow valve on the manifold and connect to a cold mains tap
    4. Connect a hose to the drain off point on the manifold and take out to waste
    5. Turn the cold tap on, open both the taps, drain off point and the flow point and flush the water through that zone

    Once the air bubbles have been removed you can then turn off the valves and the cold tap and disconnect the hose. A qualified plumber is best to carry out this task.

  • Wiring issue: faulty connection – dry joint
    This could be to do with an actuator, thermostat or wiring board. As an electrical issue it is best to contact a qualified electrician to resolve the problem.
  • Thermostat not set up correctly (E1 and E2 errors)
    Most thermostat errors will be displayed on the face of the stat. Simply reset the thermostat following the user guide to clear the error. We’ve produced some videos to help you with this process for the neoStat and PbS – click here to view.
  • Flow gauges not opened up correctly on manifold
    You will need to adjust the flow rates on the manifold. To do this, refer to the UFH manual for the system as manifolds can vary.


Underfloor heating multiple zones/entire system is not heating up

You may also find that multiple zones or an entire UFH system is not heating up as it should. There are a few reasons why this may be happening:

  • Circulation pump failure
    The circulation pump may have failed. This is an electrical issue, so it is best to consult a qualified electrician.
  • Pump relay on wiring boards
    This is another electrical issue that ought to be checked by a qualified electrician.
  • Isolation valves closed on the manifold
    The isolation valve lever should be in line with the pipework on the manifold, in the open position. If an isolation valve is closed it will be at 90 degrees on the pipework.
  • Blending valve pin stuck
    To resolve this issue you should remove the white thermostatic valve head and check that the pin valve is not stuck. If it’s stuck down it can be freed using a silicone spray. You can also use a pair of long nose pliers to try and free the pin before replacing the thermostatic head.
  • Boiler not firing (no signal)
    In this situation you will need to consult a qualified electrician who will check the wiring board connections and relays.
  • No power to the wiring boards
    Check that the main isolating switch supply is switched on. If it is off, call a qualified electrician.


The underfloor heating pump is running all the time

If you come across this issue, it could be because:

  • The pump relay is stuck on the wiring board
    Again, this is an electrical issue and so a qualified electrician should be called.
  • Faulty thermostat
    As mentioned earlier, you can easily reset a thermostat by following the user guide. It’s also a good idea to check batteries if the system uses a wireless, battery-powered thermostat.
  • Faulty actuator
    If an actuator has failed, this is most likely due to an electrical issue that could relate to a thermostat or wiring board. You should consult a qualified electrician.


Blog pressure test

Rise in pressure on the system

There are a few potential issues that could be causing the system to rise in pressure:

  • The filling loop has been left on or is letting by
    Check that the valves at either end of the flexible hose are closed, and disconnect the filling loop.
  • There is a restriction in the pipework
    If the pressure remains high even when the system is off, then pipework restriction is unlikely to be the cause. However, if the pressure varies by changing the pump speed (or switching the pump off) then there is likely to be a restriction – either a blockage or air locks. It’s important to note that if the pump is plumbed in close to the value, there will be an initial pressure rise or drop on start up.
  • Expansion vessel failed (diaphragm damaged)
    To test if this is the case, depress the needle in the Schrader valve on the underside of the expansion vessel. If water escapes, the diaphragm within the vessel will have ruptured and the whole vessel will need to be replaced. Alternatively, the diaphragm may just be empty of air, meaning there is no room for the water to expand as it heats, resulting in increasing pressure. Relieve some of the water pressure via the pressure relief valve and then connect a foot pump to the vessel’s Schrader valve, pumping it up to 2 bar. Re-fill the water side up to normal working pressure.


Pressure loss on system (boiler locks out on low pressure)

Rather than a rise in pressure, you may find that the system is losing pressure. There are a few ways that you can identify what is causing this:

  1. Check over the system for any leaks on pipework, manifolds and cylinder. This includes a quick look over the pressure relief valve, automatic air vent and expansion vessel.
  2. Re-pressurise the system (refer to manual) and isolate all manifolds. Check which side on the manifold drops in pressure. This will help you to identify where the leak is.
  3. Check the temperature/pressure relief vale is not letting by to waste.
  4. Check that the expansion vessel on boiler side is not letting by.
  5. Check that the boiler blow off valve is not letting by.

All of the above should be carried out by a qualified plumber.

If you are trouble-shooting a Nu-Heat UFH system, you can always call our Technical Team on 01404 540650.

Project advice

Contact us on 01404 549770 to discuss the best underfloor heating and renewable solutions for your project. You can also send us your project plans for a free bespoke quote.

Stacey Callun

Stacey Callun

Stacey is Nu-Heat's PR & Marketing Executive, responsible for the fulfillment and coordination of all PR activities, editorial and marketing projects.

44 comments on “Potential underfloor heating problems and how to solve them

    1. Hello Peter

      Your actuator will either have a window that a red flag moves into or, depending on the type and age of the actuator, a pin or disc will rise from the top. See our parts pages for photos of the various actuators we have had through the years: http://www.nu-heat.co.uk/s.nl/it.A/id.1421/.f?=f&sc=7&category=4061587

      If your UFH pump is running constantly then this suggests another issue – are you able to turn off/down all the thermostats? Does this stop the pump running? If not, it sounds like a relay has become stuck somewhere and you might need an electrician to investigate further.

      Please call our technical support team to discuss this further on 01404 540745


      1. Hi there, I have a problem with the bathroom floor stuck on. We recently had a power flush, and a new pump and blend valve fitted. Since then downstairs is much warmer but the bathroom floor is very hot and won’t switch off. even with the thermostat turned right down. When i turn it down the light goes off and the pump stops.(assuming other zones are off). any ideas what this could be?
        Many thanks
        Jamie Clegg

        1. Hi Jamie,

          Based on the symptoms you’ve described, we would suggest checking that the actuator is fully secured onto the manifold. You can do this by opening the actuator by turning the room stat up to call for heat (it will take about 4 minutes to open). Once open, check that the actuator is securely screwed onto its thread. If isn’t, the actuator won’t fully close the pin valve and will let water by.

          It’s also worth checking that the actuators haven’t been switched onto the port for another zone. If this were the case, the bathroom heating will appear to operate seemingly without any form of control. To check this you need to turn all of the room thermostats down and leave the floor to cool. You can then turn the room thermostat in the bathroom up to call for heat and the floor should respond. If not, and you notice another area warming, then it is a case of placing the correct actuator on the correct port of the manifold.

          I hope this helps.


  1. Hi our underfloor heating is coming on even though there is no signal to do so from the wireless control panel. Do you know why?

  2. Hi
    Our underfloor heating has been perm on since yesterday afternoon and it is at 34 degrees! As we moved into the house after it was installed we dont have a manual for the thermastat. Im stuck what to do and worried to leave the house to go to work and leave it the way it is. Ive took the batteries out of the thermastat as cant see anywere how to turn it off. Can you please advise if by taking the batteries out whether this will turn the heating off? And what to do next.

    1. If you can give us some more information we can provide you with a set of bespoke manuals for your system – please contact our technical team on 01404 540 745 and they will be able to help you.

      In general terms, as the thermostat has batteries I am assuming that it is one of the programmable types?

      The first thing to do would be to re-insert the batteries – the display will then show the current room temperature. If the thermostat is calling for heat there will be a flame symbol displayed on the LCD. If this is the case, pressing the up or down arrows will change the display to show the current target temperature, i.e. the temperature that the heating system is trying to achieve. This should have a value higher than the current room temperature.

      Pressing the down button will reduce the target temperature – keep pressing this button until the target temperature is set to somewhere between 16 and 21 degrees, or at least below the current room temperature, depending on comfort levels required. To facilitate the change, either leave the thermostat to revert to the room temperature naturally for the Danfoss type of thermostat, or if there is a tick button, like the Nu-Heat branded thermostats, press the tick to confirm the change. The call for heat flame symbol should then disappear. Depending on the type of thermostat there may be an audible click, but this is nothing to worry about, it is the switch in the thermostat switching off.

      I hope this helps!

  3. Hey – I have a two zone set up. Fired up last night. Zone one no problem. Zone two: feed pipes hot, return pipes cold, floor obviously cold. Valve opened the only difference I can see is in the flow gauges. On the cold zone flow gauge is only half filled with water and the spring with the red top does not contract to indicate flow. What’s is happening? I am a single mum so….no man to contribute.

    1. Hi Anna,

      This would suggest that the pin valve is stuck. Try removing the actuator to spray some silicone spray on the pin under the actuator head. You may have to use pliers to move the pin and it would be a good idea to spray the other pin while you are there. Once the cold weather passes it would be worth replacing the stuck valve.

      I hope that helps and apologies for the delayed response.


  4. Hi – We have underfloor heating with Nu Heat dial thermostats in each room. In two separate rooms (downstairs zone), the thermostat light is green and then trips to red, both lights then go off and a short time later the green light returns. It repeats this cycle if trying to heat the room and as a result the zone is not being heated.

    Any ideas as to what it may be?

    1. Hi Stuart,

      Apologies for the delayed response. If you haven’t already done so, please give our Technical Support Team a call on 01404 549770. It sounds like the dial thermostat power supply has failed, so will need replacing.



  5. Hello, the pump on the UFH downstairs is running smoothly but on all the time and the top of the actuators is getting warm but the flow and return pipes have no heat in them. One room has a small warm area but the other rooms don’t seem to be drawing any heat. The UFH is downstairs and upstairs we have rads. The 3 way pump upstairs by the cylinder was replaced in the summer and seems to work fine except that when the thermostat switches off the pump for the rads there is a big ‘bang’ from the pump. Could this be the problem?
    The boiler fires when I switch on the UFH on the programmer so at some point the system is seeking heat…

    1. Hi Kathy,

      We would recommend that you call out a heating engineer to diagnose this. If the heating system was working before the 3 port valve was replaced, it would suggest that the wiring is incorrect. Heating electrics can be confusing without a clear wiring schematic to follow and labelled cables!

      I hope this helps and apologies for the delayed response.


  6. Hi we have just moved into a new flat and the underfloor heating only gets lukewarm in all the rooms with all the thermostats up full we left the heating on for ten hours the boiler was on all that time and made no difference the boiler is a Keston 30 combo the hot water is perfect out of the taps can you help
    Thank you very much

    1. Hi Allan,

      It’s difficult to diagnose the issue without all of the details, but it’s possible that this could be the temperature setting on the water entering the underfloor heating system. This could be the boiler that has had its water temperature turned down, or the underfloor heating temperature control valve. The boiler should be set to around 65-70 degrees and the underfloor heating valve is usually 50-55 degrees. If you have a Nu-Heat system, we would have designed it with a specific temperature in mind so please feel free to call us for support on 01404 549770. If you have a system from another supplier, it would be worth giving them a ring.

      I hope this helps and apologies for the delayed response.


  7. Hi, i have a flow valve permanently stuck in the open (full down) position and i also have one room upstairs that will not get warm despite having the room thermostat fully up. Please could you give me some guidance please.

    1. Hi Jez,

      It sounds like the pin valves are stuck in the rubber seals and require replacement. As a short term resolution you could spray some silicone spray on the pin valve itself and use some pliers to try freeing the pin. This could be the same issue but reverse for your upstairs.

      You can buy new replacement pin valves from our webstore if you know what type you need. If not, then please call us on 01404 549770 and we can help to select the right part.

      We would recommend replacing both valves and spraying the others to ensure they don’t become stuck.

      I hope this helps and apologies for the delayed response.


    1. Hi Jimmy,

      This is very unusual. If you have a Nu-Heat system then please do contact us on 01404 549770 so that we can help. We may be able to diagnose and solve your problem over the phone, or can refer you to one of our Registered Installers in your area to investigate the issue.

      I hope this helps and apologies for the delayed response.


  8. Stat calls for heat, red like comes on and no sooner had it come on it flicks off, swap stats around to see if the stat was the issue but does the same thing? What could the problem be? Accuater maybe?

    1. Hi Dan,

      It sounds like the dial thermostat power supply has failed and needs replacing. If you have a Nu-Heat system, our Technical Support Team can help on 01404 549770. If you have a system from another supplier, it’s worth giving them a call to explain the issue.

      I hope this helps and apologies for the delayed response.


  9. Hi there.
    We have a multi floor UFH system run by Wunderfloor manifolds and a heatmiser wired control centre. One of our rooms is heating up and taking all of the hot water from our buffer tank, meaning the rooms we want to heat are taking a lot longer, we are running out of hot water and our biomass pellet donsumption has trebled.
    I’ve adjusted the thermostat down to 9 degrees and waited for the wireless signal to flash and it’s made no difference.
    When I look through the window panel on the wiring centre “zone 6” ( the room in question) looks like it’s not on as the small green light on this zone is not illuminated.
    Really could do with help but nobody locally to us can help?

    Can you advise at all? Thanks so much

    1. Hi Paul,

      This sounds like a valve/actuator issue. Make sure that the actuator is on correctly and when the thermostat is not calling for heat, that it returns to a closed position. The pin valve beneath the actuator should have some movement (up and down). If the pin valve is stuck in a raised position and can’t be pushed down then spray it with some silicone spray and try using pliers to free the pin. If the actuator doesn’t return to the closed position then it will need replacing. If this is the case, it would be best to get in contact with Wundafloor for the replacement parts.

      I hope this helps.


  10. Hi

    I have tried to set up our ‘one zone’ UFH and it all seems t be set up well but the pressure gauge is showing only less than 1 bar. The floor isn’t warming up so am I right to assume that it it is due to the low pressure and if so how do I get the pressure up!

    Best wishe


    1. Hi Tim,

      1 bar pressure is OK – between 1 and 2 would be a good range to work in. Any higher than this could cause the boiler to ‘trip out’ on high pressure alarms.

      It would be good to check that the thermostat calls for heat and that the boiler fires. If this works then the UFH pump should also be operating and the actuator button will lift proud after around 3 minutes. When the actuator lifts you should see the flow gauge red indicator drop. If this does not move then the heated water is not flowing around the circuit. Ensure the red collar is on with the deep section of the collar up (this acts as a spanner to turn the gauge). Turn the flow gauge anti-clockwise until it is fully open and the zone should start heating up.

      I hope this helps. If you need any more assistance, please feel free to call us on 01404 549770.



    1. Hi Edward,

      We’d advise getting an electrician to check this out as a number of things could cause the fuse board to trip out. One of our customers called in with a similar issue last week and it turned out to be a fault with their oven!

      I hope this helps.


  11. Hi Stacey,

    I have an issue with my underfloor NIBE heating system. The heating in the living room is constantly on and I think the pump is now constantly running. The funny thing is the heating in other rooms in the flat is running perfectly fine (and can be controlled by the thermostat). I had an electrician out and he said the thermostat was working fine. I then had an engineer out and he said I needed to replace the ‘pcb and pump switch’, which is really expensive and I am not sure is necessary.

    What do you think is wrong with the system? What are your fees for a site visit? Do you have an office in London?

    What would

    a pcb and pump switch

    1. Hi Maria,

      It sounds like this could be to do with the way the thermostats are set up. If so, it might be possible to resolve over the phone.

      If you have a Nu-Heat system, please give our Technical Support Team a call on 01404 549770. Ideally they will need your reference number (QR) to find your project information quickly. If not, it’s definitely worth contacting the company that designed and supplied your heating system to see if they can advise you. They should have a support service or be able to put you in touch with an experienced installer in your area to help fix the issue.

      We are based in Devon and unfortunately we are only able to arrange a site visit if you have a Nu-Heat system.

      I hope the above helps.


  12. Hello
    I have recently moved into a house with a Nu heat system. The system was originally installed in 2011 but in 2015 there was a fire and much of the house damaged. I Believe a new nu heat system was installed / replacements made this summer as the old system map of zoning doesn’t match up with the pipe labels now and / or with which valves click on when activated by the thermostats. I have the original qr codes but am not sure if a qualified installer was used for the reinstallation and don’t have any new project codes. The rooms react to the correct thermostats, hot water (55 degrees) flows through the in pipes and water of 40-45 flows out of the out pipes…..and the flow levels are all between 0.5 and 1.2 l/min but only one of the 9 zones really gets warm under foot (the smallest bathroom). The others don’t noticibly heat up, especially the other tiled bathrooms with marble floors. Any ideas why this could be? As I said hot water seems to flow through the system fine, but I don’t get the heat that is desired (or any!) underfoot. I’m wondering whether there is air in the systems as we did have a central heating pressure issue the other day? Or is it a sign that the correct installation materials were not used?

    1. Hi Jonathan,

      It sounds like there could be air in the system that requires flushing. Our Technical Support Team can provide your plumber with support over the phone to do this, just call 01404 549770. They can also give you the contact details of some of our Registered Installers in your area.

      I hope this helps.


  13. Hi,

    I changed the batteries on my thermostat this morning. Since then, system has not been responding to heating controls at all. The displays all look fine. What might it be?

    Thanks. Andrew

    1. Hi Andrew,

      It’s difficult to diagnose this without knowing a bit more about your controls. Some thermostats can require re-programming after the batteries have been replaced, so that would be a good place to start (the manual should help). If you have a Nu-Heat system and would like someone to run through it with you, we’d be happy to help on 01404 549770.

      I hope this helps.


  14. I had a Nuheats uhs fitted to my barn conversion contraflo system in 1999. I recently had my boiler replaced so the system was off for a while We are now only getting limited heating to upstairs and none to downstairs zones. An electrician has checked electrics and confirms no problems there. Any suggestions.

    1. Hi Norma,

      You may have some air in the system (this is fairly common when replacing the boiler). Your plumber will need to flush the system. Our Technical Support team are happy to talk them through this, if required, on 01404 549770.

      I hope this helps.


  15. Hello.

    I have a three zone uhf system. Each zone includes two pipe runs so we have six Watts 2 Wire Thermal Actuators arranged as three pairs and are wired to a Heatmiser UH4 wiring centre. The actuator have two lights, green to show there is power and a blue that lights when the actuator is actuated. One of the actuators seems to have a problem though… the blue light never comes on. The green light goes on and off as expected but the blue light never shows. I have changed the actuator and the wire but still the same thing happens. I have even tried wiring it to the terminals its paired actuator is wired to but it’s still the same.

    What could be the issue? As far as I can see the actuator is open as the pipe gets hot.

    Thanks for any help.

    1. Hi Simon,

      If the LED is not lighting up as it should, and you have tried to replace the actuator and wiring, it sounds like this could be an issue with the wiring centre terminals. Do the symptoms occur if the actuator is connected to a set of terminals on the UH4 that you are confident are fully operational? It would also be worthwhile checking the the actuator is properly, firmly seated on the manifold.

      I hope this helps.


  16. Hello Stacey, I have a zoned UFS and all was working fine until I had my Stanley serviced (drives UFH) the other day now the Accuator for kitchen and not drawing.No blue evident at all. I tested to see if the pins were stuck but alas that is not the problem. I did note that there is now water pooling under the actuator and think that this may be the problem. All I can think of is that the Engineer put the temperature right up to 70 on the. Would that cause the pooling? Everything else remained constant. Tried tightening the nuts but afraid to force. Any ideas? Thanks Eleanor

    1. Hello Eleanor,

      It sounds like the seals on the pin are letting by. This can be replaced and the new part you require will depend on the age of your system. If it’s a Nu-Heat system, our Technical Support Team will be able to correctly identify the component for you so that you can get this fixed. Give us a ring on 01404 549770.

      If you have a system from another supplier, it’s worth calling them as they should also be able to get the right part for you.

      I hope this helps.


  17. We have a NuHeat system installed before 2007. I ask a plumber to look at it because in one room the heat was not responding to the thermostat. He checked it and found that the the actuator had broken (cracked and therefore not sitting properly0. Unfortunately he could not fix it and I have ben trying without success to find a service engineer. Can I replace the curators myself? Is this a simple task or does it require a professional. Advice please.

    1. Hi Robert,

      You’ll need a replacement actuator (these can be bought here via our webstore). Whilst it’s straightforward to replace this, it will need to be done by a qualified electrician as the actuator has to be wired back to the wiring board.

      If the electrician needs any advice to help them fit the actuator, please feel free to contact Technical Support via 01404 549770.

      I hope this helps.


  18. have just had a new electricity meter fitted and now I am not getting any power to my prowarm digital thermostat – is this now a problem for the electricity company or the person who installed it

    1. Hi Hazel,

      If the thermostat was working fine beforehand, it would be worth contacting the electricity company first. If they are not able to help, try speaking with Prowarm or the supplier of your underfloor heating system as they should offer you some support.

      I hope this helps.


Leave a Reply to Robert Widdowson Cancel reply

Your email address will not be published. Required fields are marked *