HW works reliably, CH does not (Y-Plan, Unvented System)

[aeloen]

Hi,

With the cold weather now in full force we have been using the central heating for the first time since we moved into our house in July last year.

Previously this problem wasn't noticed as we tended to have HW and CH on simultaneously. However, with the weather being cold we have been extending the CH only by using the override or +1hr buttons. The problem is that this doesn't reliably work (or there is a delay). HW only reliably works every time.

We have a Potterton Gold System boiler, Y-Plan Unvented system (Danfoss HSA3 3 port valve) Ariston indirect HW cylinder.

After reading extensively on this forum and doing some tests of my own, I suspect the Danfoss HSA3 actuator is the culprit. I can turn the valve manually with the actuator removed with my hands, and it doesn't always seem to go to the CH only position.

I have ordered a replacement actuator but after some further experimentation tonight I'm now no longer convinced this is the problem.

When I trigger the CH only, a green light displays on the boiler instantly but the red burner light stays off (sometimes for a short period, sometimes for 5-10 mins, sometimes forever). The thermostat is cranked right up.

I'm not sure what the green light signifies (the manual says it is a CH Mode Light, but it lights up if HW only is selected too) and would like to understand this.

My understanding of a faulty actuator could be the motor isn't turning the spindles quickly enough to engage the microswitches which is why there is a delay (sometimes after a period there is enough torque to move them). However, as the boiler receives live through the 3-port valve in a CH only situation I would have expected the green light to stay off as well (but it comes on instantly even if there is a delay in the red burner light igniting).

Can anyone explain if the green light turning on instantly and the burner light not is expected behaviour or not?

Thanks - and hope my long post makes sense!

Cheers

 

[angusmcdangle]

Not sure what the green light/red light thing is...

If HW works consistently then you're likely looking at a fault with (in order of probability)...
Actuator (should get 230v) on orange wire once it motors across;
Roomstat (put link between live & switched live to link out);
Timeclock.
I've even had a faulty cylinder stat mess up heating demand.

 

[Blagard]

Assuming your CH is working fine with HW read on.

As you may have gathered, the actuator does not have to do anything with HW only, so response by the boiler will be almost instantaneous

If you select CH only the actuator has to drive the valve fully over to close the HW port before it switches the Boiler burner on - So there will always be a delay while that happens. This explains your lights query

Another feature of having CH only is that it is important that the HW off wired terminals are live. Starting from the programmer, then through the cylinder stat and finally to the motorised valve.

Typical faults where CH only does not work are a faulty actuator motor or a faulty micro switch. A replacement actuator head will resolve either of those. To a lesser degree is a fault with the Cylinder Thermostat or Programmer

I think you will find your problems resolved with the new actuator head

 

[aeloen]

Thanks - I'm hoping you are right and it's not the programmer or cylinder thermostat that has gone.

I should get the actuator tomorrow so will post at the weekend if this solved the issue or not.

Thanks again.

 

[aeloen]

Just in case anyone is interested or facing a similar problem, replacing the actuator seems to have solved the problem for now.

Another symptom of the problem, which may be of interest is that when the CH and HW were both on, but the HW was satisfied, the CH and HW both switched off. This was resolved by replacing the actuator as well.

Thanks for the help on the forum, I also found this very useful:

http://octaveblue.co.uk/c_heating/