Odd zone valve problem

[Ben565]

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 disconnect one of the zone valves (either one) then the system fires up normally.

So if I disconnect the CH zone valve, then the HW operates and the system fires up.

If I disconnect the HW zone valve, then the CH valve operates and the system fires up.

So both work as long as the other isn't connected. Both connected then neither works. Doesnt make a whole lot of sense to me

I have been away for a week, and the system has been inactive. I thought maybe one of the valves has stuck.. but clearly not.

 

[Ben565]

Its a viessmann vitodens 100 boiler by the way.

 

[Johntheo5]

Do you mean a S plan or have you got a unvented cylinder where you must have a 2 port valve as well as the mid position valve if Y plan?

 

[Ben565]

S plan sorry yes, my mistake, with a vented system.

**edited the original post now to correct

 

[Johntheo5]

So if there is a demand for say HW the HW zone valve opens but boiler will not fire unless the brown wire is disconnected from the CH valve? even if there is no call for CH.

 

[Ben565]

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.

 

[Ben565]

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 and opening correctly. Havent tried the CH one yet, but even if it is stuck open the HW should still work and fire the boiler up.

Its weird.

 

[Johntheo5]

Weird is the word, as you say, there is a permanent live grey wire to one side of the micro switch in both valves, when either (or both) open then the switch closes and the orange wire (switched live) then supplies 230V to the boiler/circpump.
Have you confirmed that there is 230V at the WC (wiring centre) terminal 10 or whatever terminal that both orange wires are connected into when the HW valve opens?.

 

[oldbutnotdead]

Hmmm, pink you say? Using that nice diagram above, do the pink cores go to the NC terminal on the microswitch? Wondering if there's some clever box of tricks connected to the NC terminals.....

 

[CBW]

Testing with a multimeter shows the HW microswitch is closing and opening correctly. Havent tried the CH one yet, but even if it is stuck open the HW should still work and fire the boiler up.

How did you test this and using which setting?

 

[Ben565]

How did you test this and using which setting?

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

 

[Ben565]

Hmmm, pink you say? Using that nice diagram above, do the pink cores go to the NC terminal on the microswitch? Wondering if there's some clever box of tricks connected to the NC terminals.....

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 zone valve motor

Going to the zone valve I have..
Green/yellow
Blue
Pink
Grey
Orange

So power is being switched to the valve motor from the bdr91. The valve is operating. The microswitch is closing.

 

[Johntheo5]

The BDR91 via the pink wire is opening the valve.
And if the orange wire (via the grey) is live when the valve is open then its (orange) other end mustn't be connected in to the boiler.

If you do a search on here under heating control then you will get plenty of help from the hundreds of Evohome owners.

Automated Home Forums

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[fixitflav]

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 zone valve motor

Going to the zone valve I have..
Green/yellow
Blue
Pink
Grey
Orange

So power is being switched to the valve motor from the bdr91. The valve is operating. The microswitch is closing.

Can you disconnect (perhaps temporarily) the Evohome, and see if the S-plan then works as its maker intended? That would narrow it down to the Evohome.

 

[Ben565]

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 then being triggered.

Having faffed around with it this morning, manually opening and closing both valves and checking out the wiring..... its now working fine. Everything connected up and working as it should

I'm just wondering if something somewhere was a bit stuck having not been used for a week. The HW valve is rather sluggish to operate. Maybe even a something in the boiler a bit stuck. Although that doesn't really explain why it fired up with only one zone valve attached but not both.

Weird, really weird. I'll ask in the evohome section just in case anyone else has come across it. I'm suspecting something just stuck after a period of inactivity