DIY Doctor

Heatmiser Thermostats After a Spark

Postby kippy-ken » Wed Feb 19, 2020 10:07 pm

Hi
I was relocating a heatmiser neostat thermostat on a stud wall. Had cut the hole, fitted the back box, rerouted the cable, re connected the wiring on the neostat, checked the wiring, flipped the breaker back on, confirmed the thermostat was powered back on and all looked good. Took the thermostat display off and went to screw the backplate back into the wall box.
That's when there was a spark, not sure how as the wiring is as it was all terminals where connected and tight.. Breaker did not trip, but I have lost the display/ power to all my neostats.
Can anyone tell we what has occurred?
Have I somehow blown all the backplates of my thermostats?
Am I now without heating control?
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Postby kippy-ken » Wed Feb 19, 2020 11:23 pm

It would know appear that the underfloor heating manifolds and boiler have also lost power.

So everything related to the heating has lost power.

All breakers are closed and every thing else else is working.

Would anyone have any idea of where to look?
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Postby ericmark » Thu Feb 20, 2020 11:23 am

Most central heating systems are supplied from a fused connection unit (FCU) with a 3 amp fuse, many boiler manufacturers actually stipulate a 3A fuse and some even a type A RCD.

So one would hope simple fuse blown.

However some times installers don't follow the rules, when I moved into this house last year I found 3 x FCU and a 13A plug all supplying power to central heating, normally we look for one point of isolation only exception is battery power, so technically I still have 10 independent power supplies to central heating, but 9 are pairs of AA batteries.

Motorised valves have V3 micro switches inside, these will only take around 3 amp, so any short circuit could damage micro switches, and some boilers do not use 230 volt control but either 24 volt or variable voltage to the ebus, get 230 volt on the extra low voltage circuits and you kiss the control board in boiler good by.

Clearly moving a thermostat should not cause a spark with power off, so you have done some thing wrong, to find out what needs some testing, and although some one trained may be able to trace with minimum equipment, in the main you need some test equipment, there is no magic cure of move wire A to point B and it will work.

Start point is google "heatmiser neostat thermostat manual" and get the instructions, it does show the power supply is independent to contacts this is called volt free, so first is check if it has supply volts, but it is also designed for electric underfloor heating so has options for floor temperature probes. Also air temperature probes.

You have to work step by step, and of course ensure the power is not on when doing anything other than testing voltage, and there is always danger so never work alone, some one must be able to call the ambulance. Since you have already made an error once not turning off power when you should have, it may be better to get some one who knows what they are doing.

Since it could be expensive, may be worth using one of the fixed price repair deals. Think British Gas do one, or at least they did. But maybe they have realised people like you call them for expensive faults.
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