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Yeh sorry wasn't the best picture

They are this type, don't know if they are good ones or not.

Its going to be hard to do any more because its working normally now. Which is what makes me think something mechanical was stuck/sticking. And zone valves are prime candidate for this.

It is connected up as a basic S-Plan system, just switched live for the zone valve is coming from a BDR91 instead of a thermostat or controller box. Theres no difference. I could disconnect the BDR91 and put a manual switch to the zone valve, but what would that prove ? We already know BDR91...

Yes there's a few different configurations possible. In my setup BDR91 is controlling the zone valves. I have one for HW and one for CH. My installer said it makes no difference if BDR91 triggers the boiler directly. Or triggers it via a zone valve. Personally I would have configured it so...

I don't think its an evohome problem. That part is operating correctly, and it's been working fine for some months now it isn't a new installation. As you said, bdr91 is operating the valve via the pink wire and both valves are operating when requested, as normal. Just that the boiler isn't...

Yes there is some clever box of tricks involved here. I have an Evohome system, the zone valves are controlled by BDR91, that part of it seems to be working in so much as they are activating the zones valves when required. Looking at it, the pink(ish) wire appears to be switched live to the...

With a multimeter, on ohms setting. System powered off and manually opening closing the valve to check function of the microswitch.

As I understand it, the grey and orange is just connected to a microswitch inside the valve. The other end goes to the boiler and thats what tells it to fire. Either CH or HW could be open or closed. Or both open, or both closed. Testing with a multimeter shows the HW microswitch is closing...

I've looking at the grey, orange, and pink to my zone valves. So if there is a demand for HW the HW zone valve opens but the boiler will not fire unless grey, orange, and pink are disconnected from the CH valve. I havent tried disconnecting the mains power to the valve.

S plan sorry yes, my mistake, with a vented system. **edited the original post now to correct

Its a viessmann vitodens 100 boiler by the way.

OK bit of an odd one (for me at least) I have a S plan system with hot water cylinder. Neither HW or CH is coming on, the thermostat/hot water call for heat, the relevant zone valve activates.... and then nothing happens. Pump doesn't come on, boiler doesn't fire. Weirdly though, if I...

I think there's probably a lot wrong with that arrangement, the tank doesn't even have a lid it's just got lagging over it. Agreed it needs re-doing with a new tank. It's finding somebody reliable to come and do it for me.

I don't know to be honest Yes will try increasing the pump speed as a test and monitoring what's happening in the tank.

I had my doubts about that too, but then I'm not an experienced tradesman. The vent and FE pipe tee off close to each other just before the pump. The system has recently been powerflushed so it ought to be fairly clear. I can't see any hot water coming out of the vent pipe, that's not to say it...

yes agree about PP1 it seemed a bit too weak when I tried it, PP2 seems perfect. Ah yes re-read what you said about wiring a valve up on the bypass to open when the CH zone valve closes. I've got two zone valves so it would have to be if BOTH DHW and CH zone valves are closed, then open the...

I did have someone come take a look at my system and check out the potential causes of hot water in my expansion tank. They told me it's because I'm running the boiler constantly, all the TRV's are closing, and I have the pump speed set too low (speed I). For reasons they didn't want to go into...

In case anyone else comes across this with the same problem. I unbound everything and deleted the whole zone in the end, set it up again and it's been working fine since. Weird.

CP1 seems to be much better thanks I've got an S Plan system, with DHW and CH zone valves, and TRV's on all but one radiator.