Intermittent Heating

[PG_TIPS]

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.

 

[Brambles]

If the system is configured as an S plan system ( 2 No. two port valves) - it is possibly the CH control valve. The thermostat calls for heat, the valve opens, but the micro switch which closes the switch to fire the boiler is not closing properly every time. However, if you trigger the DHW when the CH valve is open, the heat intended for DHW will feed the radiators as well ( because the CH valve is open).

To test this, ensure that your Unvented Cylinder is cool ( after a bath or shower). Set the CH thermostat to very high - if the boiler does not fire, trigger the DHW, if the rads heat up, turn the room thermostat to low and see if the CH valve closes and / or the rads get cool - the boiler should continue to fire to heat DHW.

The solution (if this is the cause) is to replace the CH valve actuator.

If the system is Y plan ( one three port valve ) it possibly needs the full valve replacing.

If you get a decent heating engineer, he / she should be able to resolve this fairly easily from the symptoms you have described.

When trying to analyse the fault in Alexa / remote control style systems - remember that (other than Open Therm controls) they are very simple systems that close one (or very rarely, possibly two) switches to fire the boiler. There is nothing sophisticated about them at all - but they look good.

 

[PG_TIPS]

If the system is configured as an S plan system ( 2 No. two port valves) - it is possibly the CH control valve. The thermostat calls for heat, the valve opens, but the micro switch which closes the switch to fire the boiler is not closing properly every time. However, if you trigger the DHW when the CH valve is open, the heat intended for DHW will feed the radiators as well ( because the CH valve is open).

To test this, ensure that your Unvented Cylinder is cool ( after a bath or shower). Set the CH thermostat to very high - if the boiler does not fire, trigger the DHW, if the rads heat up, turn the room thermostat to low and see if the CH valve closes and / or the rads get cool - the boiler should continue to fire to heat DHW.

The solution (if this is the cause) is to replace the CH valve actuator.

If the system is Y plan ( one three port valve ) it possibly needs the full valve replacing.

If you get a decent heating engineer, he / she should be able to resolve this fairly easily from the symptoms you have described.

When trying to analyse the fault in Alexa / remote control style systems - remember that (other than Open Therm controls) they are very simple systems that close one (or very rarely, possibly two) switches to fire the boiler. There is nothing sophisticated about them at all - but they look good.

Spot on. It was the CH control valve that was faulty. It wasn't actuating when the system put a demand on it. It would switch off but not on. Pretty much fell apart when removed according to the engineer. Replacement has cured the problem 100%. Thank you to repliers on this forum. A really positive experience for me.