Heating fine, hot water cutting out

[Agile]

X400 takes 4-5 weeks.

Tony

 

[Spiderpig]

So I'm waiting for the X400 to work its magic but now the HW is not firing at all. CH works fine. When I try to fire up HW either on timer or selecting Constant (British Gas UP1 timer) there is a relay click inside the timer but nothing at all else happens. No response from the boiler at all. With CH & HW on at the same time CH works fine but still no HW. I have changed the HW cylinder thermostat but no different. What would be the next thing to check? Thanks for your help!

 

[Spiderpig]

Is it likely to be the boiler motherboard/pcb? CH fires up great, no problem, but HW doesn't do a thing, no noise or clicking or anything from the boiler. I can get a recon pcb for £40ish so not bad, if that's likely to be the problem?
Thanks!

 

[Agile]

The boiler does not know where its heat is going to.

The problem seems more likely to do with the motor valve but other parts and connections may be involved.

Tony

 

[Spiderpig]

Thanks Tony. I figured the boiler moves the port valve based on the request from the timer? If the valve is stuck on CH when the boiler tries to switch it to HW then will the boiler just not do anything? Or am I mixed up?

 

[Spiderpig]

By the way, the reason I can't just check the valve is 'cos I don't know where it is!! Must be under floorboards somewhere. The boiler was moved to the ground floor of a two storey extension years before we moved in. The 22mm flow from boiler splits in two at a t-piece just above the boiler. One 22mm then goes up to under the floor of the room above. The other 22mm from the t-piece goes down into the floor below the boiler. The pump is on the return pipe. It all seems a bit of a nightmare All the wiring is behind plasterboard/tiling. Any clue how I can locate the three way valve?! Thanks!

 

[Agile]

The boiler only provides heat and controls the pump IF its correctly wired.

The controls operate the motor valve.

The only way to find the motor valve is to follow the flow pipe from the boiler!

Tony

 

[Spiderpig]

Hello again. Found the valves. Turns out I've got two zone valves (Honeywell 9021) instead of a single three-port. Number 1 (see images) seems to work ok and turns on/off with the central heating controller. Number 2 doesn't seem to do anything. I've switched 2 to 'manual open'. This doesn't fire the boiler (as expected) but I've cranked the heating thermostat up to make the boiler run and now there should be flow through the hot water circuit (valve 2) as well. The pipe into the hot water cylinder heats again but the pipe out is still cold for a long time so very little flow through the cylinder. Going to have to bite the bullet and disconnect the cylinder to clean the pipes I think.
Looks like I can replace the valve 2 head (e.g. http://www.uk-plumbing.com/honeywell-40003916001-replacement-powerhead-for-v4043h-p-41209.html) but access is terrible in a crawl space under the floor!
Hmm, how expensive is hot water using immersion anyway...?

Honeywell 9021 zone valves

• Spiderpig
• 19 Mar 2011
• 1

Valves installation mess

• Spiderpig
• 19 Mar 2011
• 1

 

[Agile]

Its not clear if your valves are the later type with a dimple which can have the heads replaced.

Its probably only the motor which has failed. These can be replaced.

Tony