Underfloor heating - fuse and stat are getting hot !

[ChrisRogers]

why is there a 13a FCU in the circuit if it's on it's on radial?

I'd be tempted to run the mat through a contactor and ditch the FCU and replace it with a DP switch.

 

[DIYDaddy]

why is there a 13a FCU in the circuit if it's on it's on radial?

I'd be tempted to run the mat through a contactor and ditch the FCU and replace it with a DP switch.

Originally it was wired direct from the consumer unit to the stat. The Part-P inspector recommended to our electrician that the switch should be added, not sure about whether he intended it to be fused as well. I checked the switch and it says it's DP (di-pole ?)

I was wondering if the 13a fuse is being run pretty close to its limit so it's warming up and transfering the heat up the short run of cable from the switch to the stat. I also noticed that this wire seems slightly lower guage than the one from the consumer unit.

 

[bhm1712]

what size is the cable? i might be oversizing but id probably do it in 2.5mm although 1.5mm can handle 15 amps not taking into account any insulation or being in any trunking etc..... im assuming the cables are buried in the plaster and under the flooring for a distance? with the 16a breaker im also assuming its 2.5mm

At work we have some 30kw motors which are on plug and sockets due to the system requiring hot swapping of motors if they fail, and although the sockets plugs and cables are well within the limits the plugs and sockets get very warm. I wouldnt expect to see this at home though.... a 3kw electric heater i have doesnt make the plug and socket hot.

 

[Waynewarmup]

Hi DIYDaddy,

You can guess from my username where I work. I'll help you get this sorted.
First we'd need to confirm which thermostat has been installed( you mentioned trying two) and where it has been sited within the room. If positioned next to a light switch or in a position where the sun can be shining on it both cause it to feel warmer than it should.
Also How deep is the back box (pattress box) that the thermostat is wired into?If too shallow it will also cause overheating.
What size electrical cable has been used from the fuse spur to the thermostat 1.5mm or 2.5mm?

The resistance readings that have been given for each of the heaters are incorrect (as has been pointed out by a few eagle eyes), so they need to confirm that they got the right reading with the correct size heater. I.e. the 2WPFM10 should be 27.7ohms +/- 5% and the 2WPFM5 should be 54.4ohms +/- 5% The tabulated current for these heaters is 13amps. The fuse will get very hot as it is running at it’s upper limit.

It would be better if a 20amp double pole switch is installed.

If you have time you could call the office and we'll talk it through and clarify everything, or just post here if you'd like and we will get it sorted.

 

[ricicle]

Does the heating appear to be on constantly rather than controlling. This would suggest that the UFH cannot heat the room to the desired level and thus is continually drawing around 13A through the stat contacts and FCU which will make them warm (although they should be able to take 13A indefinitely !)

 

[bhm1712]

if you look at the original post it says its on for about 30 minutes and then shuts off due to the thermostat emitting too much heat and altering the ambient temp around the sensor.

 

[bernardgreen]

How does the thermostat create heat ?

If it is electronic then heat generation suggests it is operating on the wrong voltage and the power supply for the electronics is overloaded.

If it is mechanical then it may have a small heater ( about 1/4 watt ) that compensates for the mechanical system switching on at a different temperature to that at which it switches off.

So for the thermostat to be producing noticable heat there is a fault or wiring error.

It might be that it is switching the full load current when it should only be switching a small current for a contactor coil. The full load being switched by the contactor. It is possible this massive overload of the thermostats output device is not enough to destroy it but is heating it up.
It can only create a

 

[bhm1712]

this is what we are trying to establish here.....

The thermostat is capable of switching upto 16A.

Its drawing 12/13 amps constantly whilst running and the FCU and thermostat are getting HOT. I think its just too close to the max limit on the FCU and im dubious as to the ability of the thermostat.

 

[DetlefSchmitz]

this is what we are trying to establish here.....

The thermostat is capable of switching upto 16A.

Its drawing 12/13 amps constantly whilst running and the FCU and thermostat are getting HOT. I think its just too close to the max limit on the FCU and im dubious as to the ability of the thermostat.

Or maybe it has a loose connection.

 

[17thman]

just a punt. defective 13A fuse which is conducting heat along the short cable run to the stat.

 

[bhm1712]

he has checked for loose connections.... all the detail is on the first page of the topic.

 

[17thman]

I know the tightness of connections has been verified but have you or someone screwed the terminal down onto insulation of the conductor and creating a poor connection with the copper causing the same as my post above