Underfloor heating thermostat, resets when active

[Podgkin]

Hello,
The issue is similar to this thread? Don't know what to do (or if it's the same) as there's no follow up....sorry.
https://www.diynot.com/diy/threads/underfloor-heating.301227/#post-2199695

The thermostat is a TH132-F.
Connected to a conservatory floor of approx. 10m², flexible sheets under laminate...?
Everything works OK until the flooring 'switches on'...then the unit dims, resets and starts flashing.
Could it be the same? Is there a way I can test it? I have no idea!


I'm open to suggestions.
Thanks for looking.

 

[Taylortwocities]

Is there a way I can test it? I have no idea!

Yes you can test it. You'll need a reasonably accurate ohm meter. Test the electrode firstly for continuity and the correct resistance for the mat size.
Then you'll need an Insulation Resistance tester to see if there are any faults to earth.

Its worth also testing the resistance of the temperature probe, although this shouldn't cause the effects you are seeing. Many (decent) UFH controllers actually say if the probe is faulty.

Is the supply to the UFH protected by an RCD? It should be.

 

[Podgkin]

No RCD....old house, old wiring...
How will I know the correct resistance for the mat size? I only know they are mats as the OH said that's what they laid down...
And what's an Insulation resistance tester? Sorry...only got a bit of know-how.

Cheers, @Taylortwocities.

 

[Echo the husky]

No RCD....old house, old wiring...

That's no excuse, an RCD should have been fitted to at least protect the floor heating.

How will I know the correct resistance for the mat size? I only know they are mats as the OH said that's what they laid down...

This information would have been filled in when the installer filled out the guarantee form.

And what's an Insulation resistance tester?

An instrument for measuring the resistance of insulation.

I fitted 2 of these a few weeks ago, one did not work properly. It would work for a bit then not really turn on, leaving the floor and room cold.

Both (and their floor sensors) were replaced with Myheat MH3500 controllers which solved the problem.

The only fault I can think of (other than a faulty controller) that would cause the screen to dim when the element is switched on is a loose connection somewhere on the supply side of the controller. A snubber should only really be needed if the controller switches a contactor.

 

[ericmark]

At 150W/m² which is what is normally considered as maximum to ensure floor does not exceed 40°C then likely 1500W = approx 35Ω.
An insulation tester is a meter which generates 500 volt to measure the resistance so that it will highlight any problems which would affect a 230 volt RMS supply.
The same meter that does insulation resistance also normally has a low ohm scale which uses at least 250 mA this can be used to measure supply cables and so work out volt drop.
You could also use a loop impedance tester to test incoming cables to see it there is an excessive volt drop.
The standard kit normally has three meters, the insulation resistance tester, the loop impedance tester, and the RCD tester all which you would need, and the kit is not cheap, so in real terms best option is to get an electrician in to test the installation, it will work out cheaper than buying the test kit.

For the unit to dim either there is a massive overload, or cables are massively under size, or there is a poor connection some where which could lead to fire. I would suggest considering the danger this is not a DIY job.

 

[Podgkin]

Sorry for the delay...
Thanks for the tips, team.


As another controller/unit will cost £60 or so, I have no tester (and my clever colleague is back from holidays), I'm going to get a person that can do stuff better than I.
May be able to claim on the insurance through the OH...? But I bet the excess will be just as much.

I'll let you know what happens.

Cheers, again.

 

[Podgkin]

Again, sorry for the delay:
The underfloor heating has a bad/failed connection to one row. This may have damaged our old thermostat?
However, that has been isolated and the new thermostat runs the other 2(?) rows perfectly.

FYI: We got a Beok TDS23WiFi unit...quite cheap and can be controlled from your phone.
Easy to replace (like-for-like connections) and looks nice.

Thanks.