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Central heating only switching on when hot water is on

Postby Taqi » Mon Nov 08, 2021 10:00 pm

Hi Everyone,

Very new here and a long thread, just getting all the info down. Here's hoping you can help!

I have a Worcester Greenstar 40cdi system boiler that is hard wired to a Danfoss FP715Si 2-Channel programmer for heating and hot water.

The boiler piping has a Danfoss HPA2 actuator and a Drayton ZA6 Zone valve actuator.

Initial problem - No Hot Water

HW stopped working. When I switched the HW programme to ON / ALLDAY / +1HR. The boiler wouldn't fire up - no green burner light. CH was fine - I have that to ALLDAY - I am a carer for my mother so if its too warm she can control it via the iflo thermostat.

So initially no HW but CH was working fine.

I had a look at the boiler which is located upstairs and moved the Danfoss HPA2 valve to manual, it clicked in place and within seconds the boiler fired up. 20 mins later we had Hot water - fabulous.

Not rocket science, So I figured the HPA2 is faulty, went out and purchased a new one, wired it up (Amateur handy man but I work with cars), I followed the old wiring and hey presto HW works fine on all settings ON / AUTO / ALLDAY etc.

Now a new Problem has emerged - No Central Heating

However, since replacing the Danfoss HPA2 now there's no CH. I re-checked the wiring - all good and neat.

I switched the HW off on the programmer and tried the CH programme on all the usual settings ON / ALLDAY /+1HR to see if the radiators and pipes would heat up - Nothing.

Upon investigation, when I move the Drayton ZA6 to manual it switches on. Great. But now the radiators only get hot if the HW is on and the Drayton ZA6 has to stay on manual.

If the HW is switched to ALLDAY then the CH will come on ALLDAY from 8am - 9pm (as per the first and last HW programmed times) If the HW is only on for +1hr then CH only comes on for 1hr and so on etc you get the drift.

However - when the CH is on I can't control the temperature from the thermostat . The radiators stay hot as per the control on the boiler.

Now the question is...

Do I have a faulty programmer? I don't think so - do correct me if I'm wrong - because the boiler fires up when the HW programme is selected and the right lights on the programmer click on (red). The iflo thermostat also makes the clicking noise when turning it above and below 22 degrees.

Do I need a new Drayton ZA6 Zone Valve Actuator? Will this fix it?

Would really appreciate if you could help me out here.

Many thanks everyone,
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Simply Build It

Postby ericmark » Mon Nov 15, 2021 11:39 am

I will guess a micro switch stuck in the motorised valve, on the valve there is normally a manual activation lever for bleeding the system, try latching that valve open, often with three port valve that will get heating running, but in summer you will find radiators get a little warm when it heats domestic hot water (DHW) so will need to change valve head before summer, but worth a try.
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