C/H pump not working unless HW is switched off

[masonmjs]

My system comprises a Kingspan 180L unvented hot water tank, Danfoss FP715si controller and a Bosch Worcester Greenstar Ri boiler, which works perfectly as far as I can see (and is serviced by BG every year).

The problem is that the CH pump will only start if I switch the HW to manual, if they both come on together (as programmed) the CH pump will not run with the HW on. The system uses a Center EHE0200157/U 22mm three-port, mid-position valve.

This problem started shortly after a new tank (as above) was fitted and actually did operate OK for a week or two but then it started to go wrong. Initially both CH and HW would come on OK but the CH would stop circulating after around 2 hours running and would only work if I switched HW to manual as above, now it won't even allow the CH pump to start.

HW is only heated via the boiler, I have not connected the immersion heater so it is not part of the problem and can be ruled out.

Can anyone suggest what could be wrong and how to check it please (I am a control systems engineer by discipline so hopefully I can follow guidance and test as appropriate).

Thanks in advance.

 

[masonmjs]

At the moment, until rectified, you have a mid position valve, so any fault finding will/should apply with this type of installation. You should be able to follow this link fairly logically to identify your present problem.
When you say the CH pump doesn't run then if referring to the circulation pump, the boiler isn't firing either?

Y Plan central heating system (flameport.com)

Yes that is exactly what is happening, boiler switches off, pump stops, then all is good if I switch off the HW.

 

[John.g]

Yes, understood, but is there only one (or two) 2 port valves being installed, if only one, then the diverter valve must still operate IMO as normal but with the extra security of a normally closed two port valve.

 

[masonmjs]

Yes that is exactly what is happening, boiler switches off, pump stops, then all is good if I switch off the HW.

mistake, replied to my own post

 

[masonmjs]

Yes, understood, but is there only one (or two) 2 port valves being installed, if only one, then the diverter valve must still operate IMO as normal but with the extra security of a normally closed two port valve.

the original 3-port valve is still fitted, I intend to fit an additional 2-port valve and wire up in accordance with the Kingspan installation guide.

 

[EvilDrPorkChop]

the original 3-port valve is still fitted, I intend to fit an additional 2-port valve and wire up in accordance with the Kingspan installation guide.

Don't bother, save yourself some hassle and just fit two 2 port valves. You'll regret it in the long run if you don't 😂

 

[plumbingdoctor]

Hi
Maybe your tempering valve doesn't work properly. this device can regulate the C/H of your hot water systems even with a multiple water supply