Boiler ignoring Nest demand

xper

I have a 3rd generation Nest thermostat/Heatlink connected to a Vogue S18 gas boiler with separate water and radiator circuits. Since yesterday afternoon, the heating circuit is not coming on when demanded by the set temperature on the Nest system - the Nest thermostat has spent hours on 'Heating' because the room temp was just below the scheduled set temperature while the boiler remains inactive and showing 'No Demand'. None of the system components - boiler, HeatLink controller, Nest thermostat or Nest app - is showing any error message or abnormal indicators. The boiler pressure is just over 1 bar, per normal. If I lower the temperature setting on the thermostat manually, it reacts correctly going to off and then back to the orange Heating display if I raise it again. There is a distinct click sound behind the Heatlink controller when it (should) switch on which it has always done, but the boiler doesn't react.

... except when water heating is active. When this is activated, prompted by the schedule, manual boost from the app or by manual activation using the Heatlink button, then the boiler fires up normally and the radiators heat up along with the water getting heated.

So what is going on here? I suspect it's something in the Heatlink controller as the Thermostat and Boiler are showing any error, they're just not communicating correctly apparently. Is there anything I can do here as an ordinary Joe or do I need to get a call out? My boiler service is coming up due anyway but I am not sure that this issue would be covered by that? Do I need to get a Nest specialist that can do a boiler service at the same time?

10-10-20

Can you find the zone-valve and see if it lights up when the Nest is calling for heat?

The way that these systems operate is that the nest normally controls the zone-valve directly (and not the boiler) and this has a switch within it which when closed (valve fully open) calls for the boiler to fire. If the valve is faulty then it might be opening but not switching. That would make most sense when you said that the heating operates when the hot-water is heating up as the boiler would already be under the control of the cylinder valve.

If you have a multimeter you can test the valve and it is typically an easy DIY job to replace.

xper

Thanks, that sounds like one possibility alright. Might be beyond my comfort level but will try and take a look.

would a bog standard annual service pick that up?

10-10-20

https://www.boards.ie/discussion/comment/120438165#Comment_120438165

No. It will only test and service the boiler.

youtheman

If you have zone valves then manually open one of them (with the lever). If your boiler starts for any one of the zone valves being open then you can at least confirm that your boiler is working o,k, You'll still need to do some more fault finding but at least you can rule out a boiler problem.