Heating only comes on when HW is also sellected

[hobbles]

Hi all, my problem is the CH is not coming on when selected on its own.

The boiler is a Baxi Solo HE condensing boiler and it only comes on when we selct HW as well, obviously we dont want to waste energy/money heating water when all we want is CH.

We have a room stat and regardless of its setting (in case it had reached its temp) the CH will not come on when selected on its own.

Admittedly the boiler is due an annual service and I do manually let condense water build up out the 'overflow plug on the bottom. I saw heating engineer do this when we 1st moved in the property when it locked out.

Any advise greatly received

 

[picasso]

which of these valves do you have ?

honeywell 2 port

• picasso
• 18 Oct 2010
• 31

or

honeywell 3 port

• picasso
• 18 Oct 2010
• 26

 

[hobbles]

The bottom one

 

[picasso]

Has it ever worked properly ? first impression is a wiring fault.

 

[hobbles]

Yes worked alright up till now. The system was installed 5 1/2 years ago when house was refurbed, we have lived here for 4 years now.

Had a warranty call after 18 months and Baxi replaced a part FOC, other than that been fine.

Stat operates fine, turns off when at desired temp etc. I assume the gas inlet is 1 setting for both? I mean CH doesnt require more the HW in case its a regulator or setting change or blockage only in CH mode? and not igniting or is that a fail safe in CH mode??

 

[MANDATE]

To me it sounds to be one of two things.
Either your 3 port valve is moving to mid position but not beyond, so you get HW and CH together for a limited period (until HW is satisfied)
There is a possability the grey wire is not live but doubtful if the system has been functioning OK in the past. It is more likely caused by one of the micro switches not making contact so it does not switch power to the motor to drive it forward from mid point.
Or if that micro switch does make contact and the valve does move on to CH only, then the contacts in the second micro switch may not make contact which allows power coming in from the white wire to go out through the orange wire.
Note When HW is selecteded and in demand it's the power from the cylinder stat that leads to the boiler/pump.
If HW is satisfied or not selected the stat cannot provide that power and it has to come from the valves orange wire and it cant do that if any of the micro switches fail to break or make contact.
With modern valve you should be able to replace the valve head only

 

[Blooflame]

To me it sounds to be one of two things.
Either your 3 port valve is moving to mid position but not beyond, so you get HW and CH together for a limited period (until HW is satisfied)
There is a possability the grey wire is not live but doubtful if the system has been functioning OK in the past. It is more likely caused by one of the micro switches not making contact so it does not switch power to the motor to drive it forward from mid point.
Or if that micro switch does make contact and the valve does move on to CH only, then the contacts in the second micro switch may not make contact which allows power coming in from the white wire to go out through the orange wire.
Note When HW is selecteded and in demand it's the power from the cylinder stat that leads to the boiler/pump.
If HW is satisfied or not selected the stat cannot provide that power and it has to come from the valves orange wire and it cant do that if any of the micro switches fail to break or make contact.
With modern valve you should be able to replace the valve head only

think you are bang on thee mate. I would add that with 3 port valves I have had faulty cylinder stats causing this problem also. It has exactly the effect you have described

 

[hobbles]

Now you mention it I have replaced the rod/cylinder stat before, I will get up in the loft tmoz and check it and also look at the 3 port valv and relevent wires you have pointed out.

Thanks for your advise will report on my findings.

 

[hobbles]

Update as follows:

Checked wiring once I got my head round S plan wiring, and you were spot on the Mid position actuator is not opening on call for CH.

Will fit new one next week and update.

Thanks for your advice.

 

[MANDATE]

With a 3 port valve it's a 'Y' plan.