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Discuss Electric ufh not reaching desired temperature in the Tiling over Electric Underfloor Heating area at TilersForums.com

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Apologies in advance for the long post, hope someone can advise

We've had our floor tiled a couple of weeks ago. This week we put the underfloor heating on for the first time and gradually increased the temperature by 5 degrees per day

Today we've set it to 27 degrees and it has taken 6 hours to get to 20 degrees starting from cold at 10 degrees!

Currently it is showing as 20.5 degrees but have also noticed it goes to 21 but then drops rather than increasing to the 27 degrees I've set it to

Is this normal?

We have 2 mats but one temperature sensor, we've also noticed where the mat is laid on the concrete side it is not as warm as the side where its a timber floor with concrete cement boards

Furthermore on the timber floor side some areas of the floor are considerably warmer than other areas of the same floor!?

Any ideas what could be wrong? Could it be the thermostat/sensor or something else?
 
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timeless john

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Did you see the mats laid out or do you have a plan layout?
Was there any insulation laid?
10 degrees is too cold for a start up temperature - your sensor may not be in the correct position!
 
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Did you see the mats laid out or do you have a plan layout?
Was there any insulation laid?
10 degrees is too cold for a start up temperature - your sensor may not be in the correct position!
The sensor was positioned in between the heating cables 300mm in

I saw the mat being laid down with the self adhesive mesh backing. In some instances the mesh was removed to avoid where the kitchen units and island will be placed

Would it be worth disconnecting the floor sensor from the thermostat to see if this makes a difference?
 

timeless john

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Was the floor sensor in a tube in the floor so it could be replaced if it failed?
Sometimes if the sensor is not taped to the tube when it’s connected to the supply it can be pulled out of position.
What was the power output of the mats?
How large is the floor area?
 
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Was the floor sensor in a tube in the floor so it could be replaced if it failed?
Sometimes if the sensor is not taped to the tube when it’s connected to the supply it can be pulled out of position.
What was the power output of the mats?
How large is the floor area?
Yep, it was placed into conduit and taped down

The mat on the timber floor side is 200w 6sqm and the concrete side it's 10sqm
 

timeless john

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My floors only take 30 mins or so to warm up and warm up is the term. Some UFH are tile warmers and others can provide primary heat source. Mine is 150w and set at 24/25 degrees as it never really gets any higher. If you disconnect your sensor it will overheat, especially a 200w mat over timber ( even on cement boards).
 
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My floors only take 30 mins or so to warm up and warm up is the term. Some UFH are tile warmers and others can provide primary heat source. Mine is 150w and set at 24/25 degrees as it never really gets any higher. If you disconnect your sensor it will overheat, especially a 200w mat over timber ( even on cement boards).
What I cant figure out in some areas its nice and warm as how I would expect it but in some areas of the floor its barely warm!?
 

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Can only be the way it was laid or lack of insulation. I have an area near a patio door without UFH mat and that’s where I head for when cramp sets in!
 
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Can only be the way it was laid or lack of insulation. I have an area near a patio door without UFH mat and that’s where I head for when cramp sets in!
Its the timber floor as you walk in its nice and warm but the rest of the floor on the timber side which had concrete boards is not as warm!

The concrete side of the floor is worse!
 
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Sorry to enter late in this thread but a question I have is, is the sensor over the timber floor side or the concrete floor side? If it's over the timber floor side then that area of floor around the sensor could be reaching the set temperature before other floor areas, such as the concrete floor area, and then switching of the system as programmed. Unfortunately the floor sensors only sense the immediate area where the sensor is placed and cannot sense the temperature on the other side of the floor. Dependant upon the programmer and where it is mounted ie. Does the programmer have the option to sense air temperature instead of floor temperature? And is the programmer mounted within the same roon as the underfloor system?
If the answer to both is yes then you could disconnect the floor sensor and use the programmer to sense air temperature instead. Even if only to see if it works any better that way.
The programmers that I use have both options and we mostly use the air temperature option, even though we still fit the floor sensor as an option to our customers if they wanted to go that route instead.
 
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Sorry to enter late in this thread but a question I have is, is the sensor over the timber floor side or the concrete floor side? If it's over the timber floor side then that area of floor around the sensor could be reaching the set temperature before other floor areas, such as the concrete floor area, and then switching of the system as programmed. Unfortunately the floor sensors only sense the immediate area where the sensor is placed and cannot sense the temperature on the other side of the floor. Dependant upon the programmer and where it is mounted ie. Does the programmer have the option to sense air temperature instead of floor temperature? And is the programmer mounted within the same roon as the underfloor system?
If the answer to both is yes then you could disconnect the floor sensor and use the programmer to sense air temperature instead. Even if only to see if it works any better that way.
The programmers that I use have both options and we mostly use the air temperature option, even though we still fit the floor sensor as an option to our customers if they wanted to go that route instead.
So we isolated the mat which is on the timber floor side, disconnected the sensor which only left the mat in the concrete floor side connected for approx 6 hours.

6 hours later the floor is barely warm! you can just about feel some warmth on the tiles :(

Should i leave it on longer? If so is there any risk of damage, overheating etc given that the floor sensor has been disconnected

The thermostat doesn't have an air sensor
 
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So we isolated the mat which is on the timber floor side, disconnected the sensor which only left the mat in the concrete floor side connected for approx 6 hours.

6 hours later the floor is barely warm! you can just about feel some warmth on the tiles :(

Should i leave it on longer? If so is there any risk of damage, overheating etc given that the floor sensor has been disconnected

The thermostat doesn't have an air sensor
Okay. So heating a concrete floor from cold could easily take a day or so before you may feel any serious heat through the face of the tiles. Obviously the time scale is dependant upon the floor / insulation make up below the tile (how thick is the insulation / how far below the tile is the insulation / how cold was it before switching the underfloor on etc).
You say that you are starting to feel heat at around the 6 hour point which is a good sign as it shows that it is actually heating.
You need to keep the system switched on a lot longer yet but say every hour just carry out a check of the surface temperature of the tiles in various places over the floor. If you use the back of your hand to check this and not your palm then you will have a better idea of just how warm or hot it is getting. If it feels like a snugly / comfortable warm temperature then that should be as far as it needs to get. If the temperature is really getting quite hot or too warm to be comfortable on the back of your hand then it is going too far and needs to be turned off. The temperature shouldn't be allowed to go above around 55deg's 'C' as there is a risk then of breaking down the screed below. Trust me here though, even 40deg's on the back of your hand will feel uncomfortable!

so, in carrying out the above you will confirm that that part of the system is functioning correctly.

You didn't say in which part of the floor the sensor was placed?? Was it the timber side or the concrete side??

Obviously in all of this, do be aware and remember that you now have no sensor connected so make sure you turn off the system before going to bed this evening if you carry out the above first thing in the morning.

Let me know how you get on.
 
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Okay. So heating a concrete floor from cold could easily take a day or so before you may feel any serious heat through the face of the tiles. Obviously the time scale is dependant upon the floor / insulation make up below the tile (how thick is the insulation / how far below the tile is the insulation / how cold was it before switching the underfloor on etc).
You say that you are starting to feel heat at around the 6 hour point which is a good sign as it shows that it is actually heating.
You need to keep the system switched on a lot longer yet but say every hour just carry out a check of the surface temperature of the tiles in various places over the floor. If you use the back of your hand to check this and not your palm then you will have a better idea of just how warm or hot it is getting. If it feels like a snugly / comfortable warm temperature then that should be as far as it needs to get. If the temperature is really getting quite hot or too warm to be comfortable on the back of your hand then it is going too far and needs to be turned off. The temperature shouldn't be allowed to go above around 55deg's 'C' as there is a risk then of breaking down the screed below. Trust me here though, even 40deg's on the back of your hand will feel uncomfortable!

so, in carrying out the above you will confirm that that part of the system is functioning correctly.

You didn't say in which part of the floor the sensor was placed?? Was it the timber side or the concrete side??

Obviously in all of this, do be aware and remember that you now have no sensor connected so make sure you turn off the system before going to bed this evening if you carry out the above first thing in the morning.

Let me know how you get on.

Cheers I'll do the above and report back

The floor setup is as follows

On the timber floor side it was overlaid with 6mm cement boards, primed and the mat laid on top followed by the adhesive and tiles

The floor sensor was positioned 300mm in between the heating cables on the timber floor side

The concrete side no insulation was laid as this would have increased the height of the floor. the floor was levelled using levelling compound which also encased the underfloor heating mat, followed by the adhesive and tiles.

The mat is 2mm thin 200w per sqm cable mat
 
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So we isolated the mat which is on the timber floor side, disconnected the sensor which only left the mat in the concrete floor side connected for approx 6 hours.

6 hours later the floor is barely warm! you can just about feel some warmth on the tiles :(

Should i leave it on longer? If so is there any risk of damage, overheating etc given that the floor sensor has been disconnected

The thermostat doesn't have an air sensor
I forgot to mention that the advice I have given is just an exercise purely to confirm that the system functions and will get to a temperature.
Because the sensor has been disconnected there is no over temp protection so don't leave the system running constantly unmonitored otherwise there is a risk of cooking the underfloor system.
 
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I forgot to mention that the advice I have given is just an exercise purely to confirm that the system functions and will get to a temperature.
Because the sensor has been disconnected there is no over temp protection so don't leave the system running constantly unmonitored otherwise there is a risk of cooking the underfloor system.
Yep agree, hopefully the heat comes through and will make sure i switch it off before going to bed!
 
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Cheers I'll do the above and report back

The floor setup is as follows

On the timber floor side it was overlaid with 6mm cement boards, primed and the mat laid on top followed by the adhesive and tiles

The floor sensor was positioned 300mm in between the heating cables on the timber floor side

The concrete side no insulation was laid as this would have increased the height of the floor. the floor was levelled using levelling compound which also encased the underfloor heating mat, followed by the adhesive and tiles.

The mat is 2mm thin 200w per sqm cable mat
Okay. So on the concrete side you have no insulation which means your heat losses will be very high and so warm up times will be much longer as you are heating a concrete slab instead of reflecting the heat upwards and out through the floor. It's a shame this wasn't considered as even a 6/8mm sheet of insulation would have made a big difference here so your losses would have been far less and you would have felt the benefits far quicker. This will also have an impact on your energy bill too!

Obviously, the timber floor side will heat far quicker than the concrete side, something that the installer should have known and so should have set the sensor within the concrete side and not the timber side as what happens is, the timber floor is coming up to the required temperature far quicker than the concrete side and as the sensor reads the set temperature required within the warmer floor, it then shuts off the system until it cools again. This means that the concrete side will never reach the same temperature as the timber floor because the warmer of the 2 floors is being sensed and not the cooler of the 2 floors. Had the sensor been placed within the cooler concrete floor then this would be the monitored floor, allowing it time to reach its temperature before tripping when it has reached its set temperature (hopefully that makes sense) giving you a warm concrete floor.. It should be noted though that you may not be able to set the controller at maximum for risk of overheating the timber floor side which will get hot far quicker than the concrete side and get hotter too.

There are a few options here now.

1/ increase the temperature setting on the controller to maximum, with the sensor reconnected where it is and see if this helps give time for the concrete floor side to get to a warmer temperature (it will never be the same or as warm as the timber floor side), but there is a chance that this may not come up to a nice warm temperature at all before the timber floor sensor reaches its max set temperature and shuts off, just as it does now.

2/ relocate or fit a new sensor within the concrete floor and sense this side and not the timber floor which will allow it time to come up to the set temperature. Obviously you may not be able to set the controller temp to maximum as there could be a risk of overheating the mat on the timber floor side, but you could carry out a monitored test on this to see just how hot it may get being set at maximum, just for piece of mind.

3/ fit an air sensed controller however, you may still feel a big difference in floor temperature between the timber and concrete floors. With this option though the location of the controller would need to be considered carefully and for sure needs to be in the same room as the underfloor system. Things to consider for instance is the height it is mounted from floor, it is mounted over the timber floor side of the room which may get warmer quicker, is it in a sunny spot near a window where the suns heat may affect it, will it be affected by heat from the kitchen when cooking etc.

4/ (This is drastic) run 2 independent systems, one on the timber floor side and one on the concrete floor side which in this scenario you would have 2 floors with similar temperatures as they are monitored and controlled separately. This in my opinion should have been the recommended option to you.
 
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