CH only works when HW on (no HW off on programmer)

[Martin C]

Hi - first post here

Trying to resolve an issue with our system at the moment. We have a Potterton Suprima boiler with a Sunvic 207 XLS programmer. I’m only able to get CH to work when HW is active. There is no HW off wiring into the programmer which I imagine could be the issue after doing some research.

However, something that confuses me... when I send a call for CH only this activates the micro switch in the three port valve and turns the spindle. So far so good.... but it doesn’t fire up the boiler.

Just wondered if this would be a wiring issue (due to not having a HW off lead on the programmer) or whether this could be a physical issue with the valve itself.

I’m a total novice but have been studying the Y-Plan and looking at our setup for a number of hours! I imagine a HW off wire could solve the problem but obviously it’s a big job running wires from the wiring unit in the airing cupboard upstairs to the programmer next to the boiler.

I’m about to get a Nest installed so wanted to resolve this before going ahead with that if I could. Would a Nest make any difference to the issue I have if I were to go ahead with the current way of working (having to put HW on when I want CH)

Any advice or thoughts welcomed.
Many thanks

 

[Gasmk1]

has it always done this

 

[Martin C]

has it always done this

Yeah, since we moved in around 9 years ago. Finally trying to resolve it! Thought I might as well if we’re intending on using the Nest to save some energy use.

 

[ShaunCorbs]

Could be a port valve issue eg not moving all the way to heating so the micro switch isn't contacted

 

[Martin C]

Could be a port valve issue eg not moving all the way to heating so the micro switch isn't contacted

The micro switch appears to make a good connection and I’m assuming it’s turning the valve adequately but it’s the fact it’s not firing the boiler which confuses me a bit.

 

[ShaunCorbs]

I would start testing you any good at elec fault finding ?

 

[townfanjon]

That programmer is the worse one ever made , is the valve a sunvic ?

 

[Martin C]

I’m thinking a multimeter purchase is imminent! the valve is a Honeywell as far as I recall.

 

[Martin C]

Just checking, is there any way the CH could operate independently without the HW off wire? From all diagrams I see it looks to be an essential part.

 

[garygvl]

Check on the back of the clock. Is the top dips witch set to gravity. If it is you could have had an old gravity system at some point and whoever installed the suprima set it up like this to save running a new cable