Underfloor heating mystery...

[ed-ectrician]

I was doing some outdoor lights for someone and they asked me to look at their underfloor heating. You know how it goes!!

The problem is it seems to keep cutting out and then the controller which has timer and stat on it keeps resetting itself. No trip on rcd or mcb when this happens. Ok, sounds like it's either dodgy connection somewhere, IR fault or faulty controller. They have an identical one on separate circuit nearby which works fine so i took off the controller from that and put it on in place of faulty one. Still doing the same thing! So i check soundness of connection in DP switch between faulty controller and the board. All fine. Then i IR tested from board to controller (disconnected) with switch on still no joy. Even shorted switch out and IR tested the whole lot and tested to see if controller worked with switch shorted out. Still no joy. Looked at soundness of connections in DB. All ok.

Did end to end on underfloor heating cables. 24 ohms, sounds right.

I feel like i've exhausted the possibilities. Anyone else got any ideas?!!

Thanks

 

[MDJ]

could be a loose wire regarding the 2 wire stat connection to the programmer or more likely a faulty controller, I have had both happen to me

 

[Richard Burns]

24 ohms sounds like pretty beefy underfloor heating, have you checked the rating of the controller to see if it can handle that load.
Have you tried testing the continuity of the underfloor heating while someone is walking around on the floor to see if something is shorting under pressure, or try an IR test on just the heater itself, possibly while someone is walking around in rubber shoes!
Also see if the stat is shorting once it operates, see if you can find the expected resistance of the stat when off and compare to reading.

 

[ed-ectrician]

Thanks, it cuts out all the time. Not when ppl are walking on it. All connections, from db to switch to controller to elements ok. Any other ideas?! I'll try IR testing elements though....

 

[ed-ectrician]

Ps - there are 3 elements on one controller. They are 24,24 and 8 ohms which comes out at 4.5 amps. I think next step is to stick the elements on one by one. Controller is pb130 230tr. Couldnt see a make....

 

[ed-ectrician]

http://www.aubetech.com/manuel/2/TH132-A-F-AF-230.pdf

This def looks like it, even thought that's not the model number on the unit.

 

[Philpot]

These sort of faults are always difficult but I always try and connect a meter or lamp to a couple of points on the cct. This may trace where the loss of power is. That is before and after the controller especially, as you say, if it is happening regularly. Try a lamp or meter on the connection where the actual heater cable is connected. The IR test will only show a suspect earth fault that will trip the CB or RCD but you say thy do not trip.
When you say the controller "resets itself" what exactly do you mean. Also what make/type is the controller.


Phil

 

[ed-ectrician]

It says here Our controle module TH132 A/F/AF goes blank every - FixYa to install a "snubber" - does this go in series or parallel with the load side?! - Not even heard of a snubber to be honest...

Anyone?! Sorry for these pain in the a r s e questions!!

 

[ed-ectrician]

These sort of faults are always difficult but I always try and connect a meter or lamp to a couple of points on the cct. This may trace where the loss of power is. That is before and after the controller especially, as you say, if it is happening regularly. Try a lamp or meter on the connection where the actual heater cable is connected. The IR test will only show a suspect earth fault that will trip the CB or RCD but you say thy do not trip.
When you say the controller "resets itself" what exactly do you mean. Also what make/type is the controller.


Phil

Hi Phil, thanks mate. When I say resets itself I mean it shuts down and starts again as if it lost power and then regained it one second later! This resets the clock and stat which is obviously not ideal. It does this every 2-3 seconds! Think it's a capacitor (snubber)

Check these links below. Pretty sure the cap needs to be fitted in parallel across load side.

TH132 Search Results - FixYa

 

[louy]

did a quick calculation, 24 ohms =9.5 amps, 8 ohms = 28.5 amps

 

[Richard Burns]

Ps - there are 3 elements on one controller. They are 24,24 and 8 ohms which comes out at 4.5 amps. I think next step is to stick the elements on one by one. Controller is pb130 230tr. Couldn't see a make....

I assume these elements are wired in series with each other and not in parallel.
I am not sure I can visualise the connections for series connection if you are able to measure each one individually unless there are a number of connector blocks inside the controller and each section is brought back to the controller and then connected to the next one.
If they are wired in parallel then the current would be 47 amps.

The fixya instructions for fitting a snubber are only one response from one person and only apply if there is a contactor fitted to switch the elements, this is not something that you have mentioned.
If it is present then the snubber may be a solution, if it is not then it should not be a problem.

Overall I would say that there is a design fault in the controller.

Another thought is if there is no earthing grid with the UFH then a fault could be developing which overloads the controller but does not trip the MCB and then the controller stops, the floor cools, the fault goes, the controller is on again.....

 

[ed-ectrician]

Am i right in thinking 1/rt=1/r1+1/r2+1/r3

So...

1/rt = 0.2

Rt=5

Where ami going wrong?

 

[Richard Burns]

For resistors in parallel you have the correct equation
So for your three elements you have, as you say, got an overall resistance of 5 ohms.
V/R = I
230/5 = 46 amps

If they were in series you sum the resistances and have a total of 56 ohms giving a current of 4.1 A

 

[linetech]

Some manufacturers allow their mats to be cut if I remeber rightly, it may be this mat has been cut to fit by the installer and it is not the type that can be, throughing all the ohms maths for the cable mat and install out causing the problem.. Just thought Id mention it. Not sure, I guess youd have to have all the data details & matt size and look at the floor size...

 

[ed-ectrician]

Ok they are in parallel, i was being thick - that's what 7 day weeks do to you!! they total 47 amps on a 16a breaker! Looks like 6mm cable at least it's not 2.5mm or something. She said the orig installers were cowboys and lots of electrics had to be redone. The UFH worked fine for 2 years before this current (no pun intended) fault came up though.

So today i just put them on one at a time and problem still occurring so overloading, although an issue, is not causing the prob. This is getting Very annoying, as i said it points to faulty controller but as i said i swapped the controller and it still had problems....

What next?!

Thanks a lot by the way everyone for v helpful suggestions.