Hi all,
I’m hoping someone can help me with an issue I’m having with my Nest Thermostat (3rd Gen) and hot water control. I have had the thermostat for about 6 years. The system was working fine.
The problem is that the Nest is unable to switch on the hot water independently. Neither the Boost function nor the scheduled times will fire the boiler for hot water. However, I do get hot water as a byproduct of the central heating (CH) being on. This is because the valve to the hot water cylinder is in the resting (open) state, so when CH is running, some flow diverts into the HW cylinder. I think I've become aware of the issue now because during the winter the CH was on regularly and so we always had HW - now I'm not using the CH as much and so the HW issue has become revealed - I'm not sure how long it has been going on.
When I request hot water via the Nest thermostat or app, the display turns orange and shows that HW is active, but the boiler doesn’t fire and the HW valve doesn’t move.
Here’s what I’ve tried so far:
- Replaced the Honeywell powerhead for the hot water control valve and confirmed the valve itself moves freely.
- Done a full factory reset of the Nest thermostat.
- Checked that the Heat Link clicks when the thermostat calls for hot water – it does.
- Noticed that despite the Heat Link clicking, the boiler doesn’t respond and the motorised valve does not move
- Checked the wiring as far as I can – nothing obviously wrong.
The CH side of things is working fine, and the boiler fires as expected when heating is called for. This seems to be isolated to the HW side and the Nest’s control of it.
Does anyone have any ideas what might be going wrong, or suggestions for further troubleshooting? Could this be a wiring fault between the Heat Link and the boiler/valve, or is it possible the Heat Link is faulty despite the click?
Thanks,
