Help identify/suggest replacement for wiring board (8-e91-12-102)

29 Oct 2019
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United Kingdom

I appear to have lost power to my programmer (Honeywell ST699) after one of my wall thermostats got knocked clean off the wall and something went pop.

I'm hoping it's the fuse in the wiring board that's blown but I've none at home as yet to test with and my father, who's on holiday, has my multimeter at present! :mad: (never lend parents tools!)

If it's the actual wiring board that's gone, could anybody here help identify it and suggest whether it is fixable or replaceable with something new please?

All I can identify is "Rehau" on the shiny silver outer case and the text 8-E91-12-102 on the board as per the image.

My wall thermostats are these I believe:-

I've been considering replacing the thermostats anyway as at least 2 of them don't seem to work (i've 6 zones yet two of the actuators never open for the underfloor heating when the thermostats are turned up) so now might be a good idea to try and sell the idea to the missus!

Any info would be great.



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Oh, and daft follow up question...

would this be a job for a plumber with electrical certs or an electrician with plumbing certs ?
Usually anyone with the correct knowledge and competence. Looks like x2 fuses could be missing? Not sure about a board replacement.
Always a bad idea to use yellow and green conductor as a switch conductor.
Meter will be needed to identify what is wrong. Looks like termination blocks might also be an issue
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So, you have lost power to the programmer (Honeywell) but it's the thermostat (Rehau) that was damaged. Therefore as the programmer provides power to the thermostat, the first thing I would check (after fixing the thermostat) is the main 3A fuse in the spur supplying the whole boiler / heating system.

It's unlikely that a fuse in the boiler would go because of a fault with the external controls, because the boiler is downstream of them. And if you have a Y-Plan / S-Plan system, the the controls are connected to a motorised valve and not to the boiler anyway.

I assume the picture of the PCB is from your boiler.

If the thermostat is damaged then I would replace it not fix it. It doesn't have to be one of the same make.
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Thanks for the replies.

I swapped out the fuse (T4AH250V) to the wiring board and whilst that seems to have got me somewhere - the green light to one of the red grundfos pumps comes on now, the programmer is still off so I'm going to assume it's toast and needs replacing by a compentent pro.

I assume the picture of the PCB is from your boiler.

The picture is of a generic rehau cased wiring board that sits (to me) in the middle of everything... several cables to the room thermostats, several cables connect to actuators on the underfloor heating manifold etc. Looks like cabling from the programmer, wiring board and then the actual boiler, valve and red grundfos pumps someone wired to a junction box of sorts which cables back to the wiring board - suggests they all draw their power from the 240V mains.

The whole thing is a bit of a spaghetti junciton of mess so probably not hurt to have the pro look at the remaining thermostats, check the wiring and termination blocks too and determine if anything else is amiss - then look at replacing the programmer.

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