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Discuss Insulation resistance check in the Electric Underfloor Heating Wiring area at ElectriciansForums.net

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Hi - I have a Warm-up underfloor heating system. And it's stopped working. I did a basic resistance check - and clearly there's a problem (shows just 18ohms when it should be nearer 200). Warmup have said they can send an engineer around to lift a tile after doing a thermo heat check. However, they said the best thing to do first is an insulation resistance check... Never done one before, but I see there are some meters online for around £35. I'm assuming to do this you:
  1. Turn off mains
  2. Remove warmup live, neutral, earth cables from connecting to the mains (completely isolates the heating elements/Warmup system)
  3. With the tester and isolated system, test:
    1. live/neutral at 1000volts;
    2. live/earth at a 1000 volts
  4. Reading should be around 200 megaOhms.
Is this correct - or is it even worth doing, given the floor isn't heating anyway...??

thanks for any advice
Rob
 

littlespark

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Arms Access
Do you know a local electrician with test equipment?
The ones we use are calibrated yearly, and cost a lot more than £35.
 

littlespark

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Arms Access
Will the £35 ones give out 1000V?
A pro tester will give 250v, 500v and 1000V
What did you use to get your 18 ohm reading?

If the engineer is coming out, he will have the required tester needed. Is the system under warranty?
 

telectrix

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Arms Access
what is the area of the mat, in sq.m.? 18 ohms equates to about 3kW which would be 15 - 20 sq.m.
 

TonyMitchell

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Arms Access
Do you happen to have kept the booklet from when it was new and installed? There’s a table showing the target resistance for the various sizes of mat and a section where you record the resistance before cutting it and sticking it down.
 
  • Thread Starter Thread Starter
  • #7
Telectrix/Tony: it's only 2.5sqm really. It's the warmup loose-wire UFH - DWS400, with the expected resistance of 128 Ohms (i'm only reading under 20..) See second row in table attached
thanks all...
Rob

Capture.PNG
Post automatically merged:

Littlespark: the insulation resistance tester was this one...: here
The system is only under warranty if when Warmup turn up they find a fault with the unit. However, I can't see how they'd identify whether it's the UFH wiring being at fault or was caused by the tiler (me...) nipping the cable whilst originally laying the floor. I just get a feeling they'll say it's not their product - which'll cost £300 to find the fault, lift the tile and fix it.. I will still have to make good and retile.
 

telectrix

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Arms Access
Telectrix/Tony: it's only 2.5sqm really. It's the warmup loose-wire UFH - DWS400, with the expected resistance of 128 Ohms (i'm only reading under 20..) See second row in table attached
thanks all...
Rob

View attachment 51935
Post automatically merged:

Littlespark: the insulation resistance tester was this one...: here
The system is only under warranty if when Warmup turn up they find a fault with the unit. However, I can't see how they'd identify whether it's the UFH wiring being at fault or was caused by the tiler (me...) nipping the cable whilst originally laying the floor. I just get a feeling they'll say it's not their product - which'll cost £300 to find the fault, lift the tile and fix it.. I will still have to make good and retile.
i'd not bother with that cost . just buy a pair of woolly socks.
 

Wilko

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Arms Access
Hi - not doubting your measurements, but have you checked the fuse has not melted? Someone on here may be nearby and be willing to test the ufh for you, if you’d like.
 
  • Thread Starter Thread Starter
  • #10
Hi - not doubting your measurements, but have you checked the fuse has not melted? Someone on here may be nearby and be willing to test the ufh for you, if you’d like.
Wilko thanks. Think the only fuse is the 13amp to the unit. I’m getting mains power to it and the thermostat is working fine. So assume that’s everything. anyone who’s in the south west London area is welcome. Based in Fulham. Thanks again...
 

telectrix

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Arms Access
if the element is shorted giving 18 ohms, it will pull 13A an the 18ohm section will get hot.
 
  • Thread Starter Thread Starter
  • #13
Tony thanks. The FCU has a 3A fuse ((checked it yesterday) and is working fine. There’s also a 5A fused socket just ahead of the thermostat... if that makes sense.
 

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