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

 

[pennywise]

Have you tested the floor probe that's set in the floor? Sometimes with UFH programmers if they don't sense that the probes working they switch off, then try to reset. I know timeguard controllers do this.

 

[ed-ectrician]

Thanks mate but... No floor sensor fitted, the controller has sensor in it built into unit which detects ambient temp.

 

[Rauer]

I've been told ( by the technical helpline) to bend the pins a little on the front plate as the connection is sometimes not very good!!!

 

[ed-ectrician]

Thanks loads for calling them rauer! I actually took the whole 2 part unit and swapped it round. So cant be pins! Is it rip out the feed and start again time?!?!

 

[ed-ectrician]

By the way, this is a sub question but if i cant solve this i've spent 3 hours on it so far, will prob spend longer as my pride is at stake here!!!!

I feel like a right 'see you next tuesday' billing for this time if it's not sorted. What would you do?!?!

 

[ed-ectrician]

Yes mate tried all possibilities it's driving me loooopy!!

 

[ed-ectrician]

Weird thing is it worked ok for 2 yrs then went wrong. Too much water when washing etc would cause rcd to trip but both rcd and mcb are ok!!

 

[bugsy]

Is it possible there is a fracture of the element which when underload (heating ) breaks causing an open circuit as the element expands .

 

[Richard Burns]

You need to review the whole circuit and mat again.

You have a 30mA RCD protected circuit a 16A MCB a 6mm² cable (single radial I assume) connected to a switch of some sort and then to a power backbox (connected correctly? the power back box should not be able to take 6mm² cables) then the controller is fitted on the back box (how is the controller set up? Are there jumper switches? what are the displays if any on the controller on start up?) the controller is designed to take no more than 16A.
From the power box there are three pairs of wires each pair going to one of three underfloor heating mats (in the same room?), there are some unused terminals for a floor sensor (possibly) and (possibly) a pilot wire terminal unused.
There is no floor sensor (is the controller temperature sensor clear of dust and debris)
The floor heating mats appear to be 2 x 2.2kW and 1 x 6.6kW(really?), it is not known if there is an earthing grid associated with the mats, make of the mats is unknown.

There does not appear to be an earth fault as the RCD does not trip.
The current anticipated would trip a 16A MCB in about 10 seconds. The measured current on start up is not known.
The controller has been working for 2 years satisfactorily but has (in the last ....days) stopped working and when powered up starts and then cuts out, then starts, then cuts out...... (possibly not calling for heat yet and so not tripping MCB, but MCB was holding when it was working, is the controller staged i.e. only powering the mats by PWM or such like)

The heating mats have individual continuity on each (24, 24 , 8 ohms).
The insulation resistance of the mats is unknown.
The insulation resistance of the circuit up to the power box with and without the switch is OK.
The controller and power box from another location, where they are working, have been used in place of the original and the fault recurs (so the fault is not in the controller or back box).
The instructions state that when using a contactor (not used in this instance?) a snubber should be fitted across the load terminals.
When each mat is connected individually the fault recurs (so not a current loading issue)(only a triple fault on every the mats or a cross connection between the mats could cause this if the fault is in the mats.)


[Right no faults on fixed wiring, controller or mats (except loading), your heating is fine madam, that will be £250, oh yes the resetting? it is typical of these units, just ignore it, that is what I am going to do!:nonod:]



Does the controller start up OK without the mats connected?
Does this controller work in the other location?
Do you have the specs / instructions for the controller, power box or mats that you can compare to current readings?
Did anything change just before the heating failed (any work DIY or Professional)?


Well I give up!

 

[pennywise]

I vote for ripping the floor up and making a visual inspection

 

[pennywise]

I know it's a simple thing but has the programmer been set to remote stat and not on floor probe mode, sorry you've probably been there for hours going through every permutation so this is probably a moot point.

 

[ed-ectrician]

i think I might just keep repeating "It's not your fault" over and over again until she cries...

not your fault (Good Will Hunting) - YouTube

Seriously though I think it's ripping up floor and rewiring time....

Far too much load on one 15a controller anyway, it's no wonder it's not working for one reason or another. I can bill for my fault finding and advise to rewire. I'm not doing it though, sounds like a right pain in the arse and I'm too busy haha!

Seriously everyone thanks LOADS (pun?!) for your help on this. It makes me feel better knowing I have tried all the likely things and done what you guys would've done too. Makes me feel like less of a failure

Ed

 

[ed-ectrician]

I know it's a simple thing but has the programmer been set to remote stat and not on floor probe mode, sorry you've probably been there for hours going through every permutation so this is probably a moot point.

Yeah I checked this, thanks mate. I love pennywise too. And NOFX etc - reminds me of my youth! Went to see them all and lagwagon at deconstruction tour in east london when i was like 16 and a right little punker!

 

[pennywise]

Yeah I checked this, thanks mate. I love pennywise too. And NOFX etc - reminds me of my youth! Went to see them all and lagwagon at deconstruction tour in east london when i was like 16 and a right little punker!

I only got to see Pennywise once with Jim Limburg still fronting them and a couple of times since with the new guys, it's not the same having said that the new singer sounds like dexster holland so it's should be the perfect combination of the offspring and Pennywise but it just doesn't work . I saw NOFX this year at download festival very funny and always good. Hopefully bad religion will be touring next year

 

[ed-ectrician]

For anyone who's interested i switched round controller today just like i did first last sat and it was fine. Strange! Bought new controller working all good now!! Thanks gents. Ed