Radiators hot only when hot water turned on


Postby martynl » Tue Aug 11, 2009 9:46 pm

My central heating / hot water boiler will only heat the radiators if the hot water is turned on.
Turning on the central heating alone gives no response from the boiler.
Turning on the hot water alone heats both hot water and radiators.
Turning on both heats both also.

Boiler is 2 years old Ideal Icos (not combi)

Programmer (new replacement) Sunvic Select XL - I have tried removing this and shorted the terminals with wire without eliminating fault

Room Thermostat Danfoss RF1 (radio) the receiver indicates heating on correctly.

Danfoss H-series 3-way valve in loft - valve seems to move freely if motor unit removed.

What area should I be looking in to resolve the problem?
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Postby plumbbob » Tue Aug 11, 2009 11:23 pm

You have omitted a most important piece of information. Is this a new fault, or has it always been this way? Has it occurred since the new programmer was installed?

The most likely culprit is a wiring error or fault but it could be a faulty 3PV or tank thermostat.

The question is, how competent are you with wiring? It is not just the danger of electrics, but heating wiring is very complicated to anyone not familiar with the snarl of wires found in most wiring centres.

If it were me, I would head straight for the programmer and examine for correct wiring.

If you feel up to it, google this octaveblue.co.uk/c_heating/index.htm for the most likely wiring scenario.
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Postby martynl » Wed Aug 12, 2009 7:00 pm

Thank you for your reply.
This was a new installation (including all wiring) 2 years ago. So worked perfectly before.

Like you I thought the programmer was ay fault, hence new one fitted of same model.
Removing the programmer and shorting the terminals (effectively romoving programmer from the system) to force the CH on does not alter the fault.

I currently suspect the 3PV but unsure if just the motor or faulty valve.
I will check out the wiring scenarios you suggest.

Any further pointers will be gratefully received.
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Postby htg engineer » Sun Aug 16, 2009 1:48 pm

Remove motorised valve/actuator, then try turning the valve spindle - if it turns freely then it's probably just the motorised valve at fault - replace.


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Postby martynl » Fri Aug 21, 2009 4:07 pm

Thanks for all your help so far. Had some time free to try a little diagnostics.
As before removing the programmer and shorting the link to force CH on did not cure.
Removing the RF Thermostat receiver and shorting lin to force CH Call did not cure fault.
Checked out 3 port valve in loft.
Spindle appears to move freely (to my untrained touch).
Regardless of position of spindle if HW turned on pump runs and lever moves to HW position.
If HW OFF and CH ON - pump does not run - spindle will not move from HW. If moved by hand lever pulls back to HW - once you get to centre position lever goes slack and does not return to HW until HW turned on again.
I am going to order replacement motor but can you explain why the pump fails to run if CH ON.
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Postby plumbbob » Sun Aug 23, 2009 10:25 pm

Shorting the link you describe won't switch the heating on. In a "Y" plan system the pump is not controlled directly from the timer, but from the three port valve.

To force the pump operation, the HW N/C timer contacts have to be shorted as well as the N/O heating contacts.

I still think you have a wiring problem. Have you confirmed the correct installation of the programmer????
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