UFH mat blowing fuse.

[Sean Kelly]

The dread strikes when the number of a customer appears on your phone several months after you have done work for them.

This happened to me yesterday when a customer stated that her UFH is now blowing the fuses in her house.

I completed the job in May’14 and had a continuity test running on the mat from start to completion of job. I also took resistance readings before/during/after installation. These readings matched the mats documentation. I left the readings for the electrician. The usual spiel about turning it on gradually etc was given to the customer.

To be fair, the customer was ringing me for the name & number of the mats makers.

The mat was stuck to 18mm ply, then SLC, then 60x60 porcs in the kitchen.

Just by chance, the electrician was there and he stated that the continuity test was fine, but when he put a high volt through the cable it showed a possible crack in the insulation.

I’m not a sparky, but what else can I do at installation stage when all the readings are fine.

I believe that they tested the mat in May and it was fine.

Strangely enough their previous ufh mat did the same thing. It was down for 5 years then developed a fault where it kept blowing the fuse – possible connection?

Has anyone else come across this scenario?

 

[radim]

who is manufacturer? warm up offers lifetime guarantee so I would giv them a call.
you say that it blows fuses in the house - there ishould be a fuse box below thermostat. On houses I work is anyway...

 

[Sean Kelly]

'Prowarm' from the Underfloor Heating Store. As far as I remember there was a spur that the cables went into, but I did not touch that part of the system. Lifetime guarantee is a bit sketchy when it comes to an already installed system. Will let the customer deal with the company as I don't know exactly what the electrician has done.

 

[White Room]

I'd be getting a sparky in...

 

[Time's Ran Out]

How big was the mat in respect of amps and the load it would have put on the ring main ?
Was the plywood acclimatised to the room before it was fixed?
Did the customer send off the documentation for their guarantee?

 

[Sean Kelly]

How big was the mat in respect of amps and the load it would have put on the ring main ?
Was the plywood acclimatised to the room before it was fixed?
Did the customer send off the documentation for their guarantee?

200w 6 mtr mat. Ply down for About 10 years. Don't know if customer sent off docs.

 

[Diggy]

Is it blowing the fuse on the fused switch spur or the main fuse board?

Just interested to know , not a sparky , but nice to know of diffo scenarios for anything in the future.

Diggy

 

[Sean Kelly]

Don't know Diggy, but I've given the customer contact details etc of the UFH company . I've also asked her to keep me posted because if the resistance is good and the continuity is good there is nothing more I can check.

 

[Sean Kelly]

It's blowing the fuse on the main board.

The story so far. I spoke with the Underfloor heating store and they said that the cable could have had a very slight nick (a hairline crack). This crack would not show up on the resistance test nor the continuity test. It would however show up on a megger tester (250v).

When the cable heats up it expands. It makes the hairline crack open slightly, and it could be this that is causing problems.

I've put a call into Steve Ashby (he appears on several threads within this forum). He is an independent fault finder/fixer. If it is a fault with the mat then the Underfloor heating store will pay. If it is an installation fault then I will pay.

One thing that the UFH Store said to me was that the customer must fill in the lifetime guarantee form and send it back.

The only thing that is nagging me is that the main consumer board is blowing. Is this normal? I would have thought that only the spur fuse would blow.

 

[Time's Ran Out]

200w 6 mtr mat. Ply down for About 10 years. Don't know if customer sent off docs.

200w mat is for concrete not wood. Expansion in the heating up may open the joints in the plywood and split the cable. Without the guarantee being sent off there is no recourse.
But then again the shop may accept responsibility!

 

[lizzardtong]

It's blowing the fuse on the main board.
The only thing that is nagging me is that the main consumer board is blowing. Is this normal? I would have thought that only the spur fuse would blow.

is it blowing MCB OR RCB in consumer unit?

 

[Diggy]

If its on the main board then surely it must be in the wiring after the FSS , and therefore probably nout to do with you.
If it's in the UFH then the fuse in the FSS would blow wouldn't it?

My 50p is on a nicked neutral somewhere down the line between the other side of the FSS and the main board. :0)


Thats my guess anyway as a non sparky anyhow. :0)

Keep us informed.

Good luck

Diggy

 

[Sean Kelly]

Arggh……………………it was my fault!

I met up with Steve Ashby just before Xmas. What a nice chap he is. His equipment is basically a Ghost Busters kit with dials and probes, wires and bleeping devices etc. It did not take him too long to find the fault. I always take photos of UFH cables prior to SLC. This helped speed up the diagnostics.

He had to remove a tile and some skirting by the back door. He removed the termination crimped end of the cable and re-crimped it with a thinner crimp. This slimmer crimp did not protrude as much as the last one. He then used a cable pin and pinned it to the plywood floor.

The first picture (which was taken at installation) shows the end of the mat terminating by the back door. Well, it’s actually terminating in a void under the skirting. So basically, the last 2 inches of the cable is neatly tucked out of sight. Why did I do it?................I did it because the last bit of the cable is nearly always double the thickness of the wire because it has been crimped. I did not want it sticking above the SLC when it was poured.

The SLC was poured and I tiled. That was last April. The heating has been on throughout the Summer, but when it turned cold and wet that is when things went wrong.

Where I went wrong…………………The entire cable (apart from the cold tails) should be encased in SLC and/or tile adhesive. There should be no voids. What I should have done on this occasion was to make a hole in the ply and bury the end of the cable. Then cover it with SLC.

UFH cables heat up to about 70degrees. As a comparison, a hot glue gun heats up to about 120degrees.

The heat generated by the cable needs to be drawn away quickly, this is achieved by the surrounding SLC/tile adhesive and tile. The end of my cable was open to the elements. So when it heated up to 70degrees the heat built up around the cable and the resin inside the crimped cover melted. You can see the blob of resin in the second photo. The end of the cable is now even more exposed and it is drawing in moisture from the atmosphere which eventually causes failure.

So in the end it was a day of learning off Steve. It was also a day I had to hand over some money to pay Steve for his services. However, my customer said that they would pay half the costs. I was astounded. What a kind gesture………………..an offer I eventually accepted!

I chatted to Steve about the Tilersforums and he said he had heard about the forum from another tiler (I think it was Bugs183), when he cut through a cable in a doorway!

So remember to make sure the hot part of your cable is encased in concrete. Do not leave any exposed cable under cabinets or skirting (it was literally an inch of exposed wire that cost me over a days wage).

 

[Sean Page]

I attended a UFH training course run by Raychem a few years back and they showed us the thing with the Megger Tester thing.

With our normal installation tests (I do the same as you Sean) small faults in the insulation wouldn't/didn't show up but when they pumped 1000v through it you could actually hear it sparking.

I usually have one of the Warmup alarms connected when I'm tiling, but they wouldn't detect hairline fractures. When I asked they guy if there was any point to the alarms he said that as fitters we can only do so much, unless we wanted to invest a lot of money (and training) in a megger tester that would probably never really be needed.

I would push this back towards the manufacturer and hope the customer sent any guarantees off