Vaillant VCW sine 18 Pump wiring position II issue

[cakeydicko]

To anybody out there with experience on these old wonders (installed 1982!).
The boiler has 3 options for wiring (not speed settings) and works fine with the pump wired to connection I ( appropriate, according to manual when clock and roomstat fitted) or connection III ( pump running continually). But if the pump is wired to connection II ( appropriate, manual states, for my situation when just clock and TRVs fitted) then the boiler will not run continuously.
It fires up momentarily but then cuts out as soon as the pin in the solenoid valve activates the attached micro-switch which (as far as I can understand from the wiring diagram)then cuts off the neutral to the relay for the pump in position II.
The boiler is working fine at the moment for both hot water and heating but wired to option I or III only so I'm puzzled,.....what's going wrong in position II?

Any ideas greatly appreciated. Dave

 

[cross thread]

If I remember correctly position 2 is under the control of the boiler stat,but it’s been a while since I last worked on one

 

[cakeydicko]

Thanks cross thread,
I think that's about right. The service leaflet states "Setting II; For use with thermostatic radiator valve systems. Pump is switched off by clock or gas valve switch when gas valve closes".
My problem is that it appears to me that when I press the heating switch the pump starts to run, the gas valve OPENS, (necessary for combustion) but as the gas valve opens it operates the switch and breaks the neutral path for the pump relay. The pump then stops and nothing further happens. This all takes place in approx 1-2 seconds.

 

[DP]

It would be more appropriate to fit a room thermostat or programable thermostat to make better use of gas consumed and leave pump to setting 1

Setting 2 is for no room thermostat and boiler is self so trolling the burner

https://www.acwilgar.co.uk/Boiler-Manual-PDF/Vaillant/VCW Sine 18 20-1 25-1 T3W.pdf

Look at Page 19

It fires up momentarily but then cuts out as soon as the pin in the solenoid valve activates the attached micro-switch which (as far as I can understand from the wiring diagram)then cuts off the neutral to the relay for the pump in position II.

Switching is always on power side, seldom the neutral unless a solid state device is used
Look at the microswitches on top of the diverter valve under the aluminium cover for a starter

ATM pump setting 1 gets mains voltage from terminal 4 in the diagram to run the pup
Pump setting 11 is through relay (79) contact to terminal 4. If that relay is not operated, pump will not run

You may want to check DC solenoid microswitch 77 also.

 

[cakeydicko]

Thanks for your reply DP, much appreciated.
I only have TRVs and a time clock at the moment which is why I wanted to wire the pump to terminal II as per the instructions in the manual. I agree your suggestion re the roomstat is a more efficient option and is probably the way I'll go. However I'm still left with a boiler that for some reason has a fault, i.e. it should still operate with the pump wired to terminal II albeit less efficient. Re your suggestions with the micro-switches, the DC solenoid micro-switch is new and tested and I've tested both micro-switches on the flow/diverter valve and both are ok including continuity to edge connectors on PC boards. My thoughts re the neutral return from the pump relay being interrupted(and thus switching off the pump) when the solenoid energises is based on information from an old post by the "831Bunny" in which he attached a page from his vaillant training manual which shows the solenoid micro-switch and it's 3 connections ; brown wire is common neutral, black wire is neutral for the pump relay position II, blue wire is neutral for time delay discharge. Thus, as I understand that, when the switch is unmade the brown and black are connected and the relay operates the pump (as you said). That's fine but within a second or two the gas valve solenoid operates and as it does so, makes the micro-switch which disconnects brown and black and makes brown and blue and hence the pump stops.
Thanks for your help and thoughts anyway and fortunately I am able to use the boiler as it is so no worries, but just a bit of a mystery still......

 

[DP]

If the boiler works ok at pump position 1, at 2 the pump has a direct feed to pump via 79.

I would be getting the multimeter out to find out where the voltage is getting lost.

The pcb is quite straightforward too

 

[cakeydicko]

Thanks again DP but if you could bear with me. I'm still puzzled (and sorry if missing something obvious) about your last post.
Yes, I agree that the pump has a direct feed from position 2 via 79 (the relay) but isn't that only true whilst the solenoid microswitch is in it's unmade state -which it is initially before I turn on the heating- and the relay coil current can flow keeping the relay contacts closed and the pump current flowing. However, when I turn on the heating switch, within seconds the gas valve solenoid operates to regulate the valve and in so doing it (via a small horizontal pushrod) "makes" the solenoid microswitch and interrupts the current to the relay coil. Consequently the relay contacts then open and the direct feed to the pump of the mains voltage is broken.
I've attached another schematic which might make my analysis clearer but would apprectiate any further thoughts you may have?