Potterton boiler - CH but no HW

I must say I fail to see how he can cock up the electrics this badly simply by changing the thermocouple.

There should be no touching of the electrics for this? Unless he has disturbed the three conductors in the gas valve IF he withdrew the burners. Perhaps the earth is touching one of the other terminals.

Perhaps this has blown the microswitch in the zone valve. But any engineer with half a brain sould be able to trace a fault like this if only by disconnecting things systematically.

Or perhaps I've missed something - I do wish people would use paragraphs in their posts...
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I've turned off the HW and then the power, but there is still no resistance in the valve so it seems it isn't working. Can I check one last thing? Is it possibly the wiring, or wouldn't the plumber have touched that when replacing the synchro motor?
I'm really grateful for the advice! I'm not trying to avoid paying for the work, but I just want to make sure it's done properly. I'm also conscious and a bit embarrassed that this is free advice you are giving me!
Thanks again.
Sorry didn't see that he had changed the motor.

The lack of resistance implies that the mechanism in the valve head is not correctly assembled - again quite how he has mangled this simple assembly I do not know.

These valves have a spring set in them which generates the resistance agaoinst the motor so that the valves pulls shut when the stat is satisfied (thus cutting power). As the valve opens (on call for heat form stat) a small foot is moved over and hits a small microswitch and relay which tells the boiler and pump to fire.

You'll need to check for 240v ac when the stat and clock are calling for heat. This should be at the brown and grey wires inside the valve head. When hte valfve is open you should have 240v ac at the orange wire. If you can trace the cables back to the wiring centre this should be a doddle to check with a multimeter - obviously if you know what you are doing; which this guy obviously doesn't.
Sounds like he has cocked this right up :eek: What a plonker. Saying that I never change the synchron motors, always the entire head.

I think this is your easiest answer as well.
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Point taken about the paragraphs. I realise you need as much info as possible without me rambling.

Dan - I'm pleased to have an explanation about how it happened in the first place. He did take out the burners when changing the thermocouple, which surprised me a bit. I'll get him (or someone else) to check for a stray contact in the gas valve.

Dave - I'd better get someone else to change the valve again.

Everything you have both said fits what I'm now finding. You should both be doctors!! Thanks to you both for your help and patience.
If you isolate your ch electrics and can follow changing one wire at a time then a new actuator is a simple job you could do yourself. (As long as you are not colour blind) No offence intended ;)
Dave - Do you mean I could just change the whole head of the zone valve? No offence taken by the way!
You really are helping!
I'm paranoid about electrical safety by the way!
Yes, unless it is a very old one such as a landis & gyr or honeywell without the dimple sticking up on the actuator, opposite the honeywell name.
I've got the original paperwork - it's a Honeywell V4043 - not sure whether it is B, C or H. But I've just looked at the Honeywell website and I can get a replacement head.

Thanks too.
I you remove the lid of the valve your should see either:

4 cross head screws


2 torx(?) screws and two locator bumps that hold the silver head to the brass body.

If the former then you need to drain down and do a conversion (actually very easy once the water is gone)

If the later then isolate power, get new head. Swap. Done.

Remember yoiu still need to ascertain what is blowing fuses etc. - or have I missed that it?
The first fuse blew when the plumber was in the boiler , so to speak, having changed the thermocouple. He quite rightly pointed out that the fuse was over-rated at 13 amp, though it had been there for 20 years! It is now 3 amp and nothing has blown since.
Thanks for the info - I think I'll have a go! :D
13amps is way too much. When that blew it could well have overloaded all the compnents :(

They are only designed to cope with a peak of 3amps. The fact that it lasted this long on 13amp is more by luck than judgement.

I am afraid you could have blown more than just a zone valve.

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