Hi, I have an unvented system in my home. The boiler is an Ideal ICOS HE15 and the controller is a Sunvic select 207XLS. My room thermostat is an aftermarket wifi unit which I can control via a phone app or voice control through my alexa. Now, here is the problem. Recently the central heating is only answering calls intermittently. The controller is working properly and my hot water is working perfectly. The heating however is not coming on (approx half the time when it gets a call from the thermostat) The thermostat is working correctly and when I alter its setting I can hear the actual click as it puts the call on the boiler. Notably if the boiler has ignored the call from the heating but I go to my cylinder cupboard and turn up my cylinder stat, the system fires up fine. It then heats the rads even if I immediately turn the cylinder stat back down it stays on because it is now seeing the call from the room stat. I am at odds to explain what the problem is and would like a professional to repair it but as it's a tricky one I'd like someone who can figure out the problem first.
Regards.
Paul.
Regards.
Paul.