Baxi 836 combi control query

[1974stephen]

I've just had a Baxi 836 combi fitted and the call for heat for the boiler is from the grey and orange closing contacts from all the zone valves. Even though on a multimeter they are showing open circuit and short circuit when there isn't and is a call for heat respectively, the boiler continues to fire even when there isn't demand. If I disconnect the wire it stops.

It's currently working with the valves held open and the call for heat taken straight off the time clock just so we can have heat after three days without!

I'm wondering whether I need to fit a relay between the zone valves and the boiler or route a 230v live through the orange and greys back to the boiler to cure the problem. Clearly it can work with a dry closing contact but the manual also says it will work with switched 230v as well.

Anyone have any ideas?

 

[denso13]

I've just had a Baxi 836 combi fitted

I don't mean to be flippant but have you asked the installer? It shouldn't need the additional relays, pretty straightforward.

 

[1974stephen]

I have; he seemed to think that it should work as wired, but doesn't normally do anything more than connecting to a wireless stat. If any more than that is required he gets an electrician in.

 

[1974stephen]

To anyone that might want to know in the future, I wired a 230v relay via the orange and grey contacts on the zone valves and then took a clean closing contact off the relay to the boiler, and this worked perfectly. There isn't a dry volt free closing contact on the boiler, it's just two contacts, 230v present on one, which when shorted to the other fires the boiler. There must be some spurious voltage being picked up somewhere, enough to trick the boiler into thinking it needs to fire.