Oil boiler - heating working but no hot water

[Andy18n]

Hi all
Odd issue with my Firebird oil boiler not working on hot water only. The boiler is not being activated (green light doesn’t come on). Heating working fine.

It’s been intermittent for a few weeks and now constant.

I have eliminated a lot of likely issues:
- hot water cylinder thermostat is fine as if you turn it down/back up you can hear it activating the motorised valve
- boiler and green light activates immediately if central heating is activated
- hot water motorised valve is working ok, have opened it fully manually to double check but boiler still doesn’t activate on hot water only
- there isn’t an airlock as I have run Fernox cleaner through it for a week, drained and flushed whole system with new inhibitor. When central heating is on I get good flow through the cylinder coil and the hot water heats very well
- opening hot water motorised valve manually still doesn’t activate boiler on hot water only
- the Honeywell controller relay is clicking as normal when the hot water is pressed on/off.

Now here’s the strange bit. I have tested the boiler on/off on the Honeywell timer several times. Occasionally if you activate the central heating and hot water the boiler starts and fires, if you turn just central heating off, it will sometimes stay on and heat the hot water fine. But next time hot water only is called via the cylinder thermostat the boiler won’t activate and no green light.

So I think it’s something to do with boiler activation signal from somewhere for hot water only.

Any ideas? Might it be the Honeywell controller/timer even though the relay is clicking?

Many thanks in advance

Andy

 

[lostinthelight]

Sounds like it could be the switch in the motorised valve which isn't activating the boiler orange wire iirc

 

[terryplumb]

Manually latching the motorised valve will not fire up the boiler ,only open it's gate to allow water to flow through it .
You would need to establish voltages present ,at various points in the wiring centre to determine where the fault is , timer,cylinder stat ,and motorised valve.

 

[Andy18n]

Sounds like it could be the switch in the motorised valve which isn't activating the boiler orange wire iirc

Thank you I didn’t realise they had a boiler activation micro switch in them. This makes a lot of sense as the motorised valve is buzzing a bit when activated. I’ll change the power head and see if it fixes it. Worst case is I end up with a V4043H spare!

 

[Andy18n]

Thanks again.
Just turned hot water only and been up and given the motorised valve (which I’d actually parted from the oipework to keep it physically open) a good clout and hot water kicked straight in!!
So it’s definitely power head micro switch.
One arriving tomorrow.
Brilliant advice thanks

 

[Stuckinarut]

Make sure you test the spindle when you change it.