Alex McLeanDoes anyone know about opentherm ? Since enabling it on our boiler (ideal c30 with hive thermostat) the boiler only switches on for a few seconds at a time (not getting beyond 21 degrees c despite opentherm flow set to maximum) and the radiators don't heat up at all. The engineer says that's just how opentherm is. #opentherm #plumbing #boilers
Ben Aveling@yaxu How far apart are the desired room temperature and the current room temperature?
@BenAveling A long way.. I've tried setting target to 32 degrees when it's been around 17 degrees in the room.
@yaxu Yikes, OK, yes. If the desired temp and actual temp are close, then the radiators should not be much more than room temp. But if they're that far apart then, yes, the radiators ought to be at least noticeably warm. Does it even hold the room in the sort of 17-21 degree range?
@BenAveling No.. I wonder if it would start working if it gets colder?
I think the possibilities are that
1/ there is just some annoying incompatibility between thermostat and boiler
2/ something in the boiler is broken in a way that only affects opentherm and not on/off mode
3/ something else
I have no way to tell which..
I think the possibilities are that
1/ there is just some annoying incompatibility between thermostat and boiler
2/ something in the boiler is broken in a way that only affects opentherm and not on/off mode
3/ something else
I have no way to tell which..
> would start working if it gets colder
If it isn't holding a specific temperature, I suspect the answer is no.
But if it keeps the room at 21 even when it's colder outside, then it sounds like it is kind of working - the radiators not being hot could just indicate that it thinks the room is at the right temperature - so it just keeps the radiators just warm enough to hold it at 21 and no warmer. If so, then the problem is that it's not respecting your desired temperature.
cont...
> annoying incompatibility
While there are plenty of boilers that aren't compatible, Ideal Combo/Combo+ C30 and Hive should be OK, at least according to (e.g.) https://www.theheatinghub.co.uk/opentherm-boilers-controls-compatibility-guide
@BenAveling Hmm all it really does is turn the boiler on for a couple of seconds then cut out momentarily saying "Room stat or timer off", then trying again ~15 seconds later
https://www.youtube.com/shorts/8PT6tUV2gug
https://www.youtube.com/shorts/8PT6tUV2gug
18 October 2025
@yaxu That's interesting. If I read it right, the number on the boiler starts at 22, counts down to 19, below the actual room temp (20.2), at which point it fires up (the fire symbol), then counts back up to 23 (the target temp), at which point it switches off. It then counts down to 18 but this time doesn't fire up.
But also, the pressure is below 1 bar?
The Ideal Logic Combi C30 boiler should be between 1 and 1.5 bar when the system is cold. When heating is on, up to 2 bar.
But also, the pressure is below 1 bar?
The Ideal Logic Combi C30 boiler should be between 1 and 1.5 bar when the system is cold. When heating is on, up to 2 bar.
@yaxu If so, might want to check that.
e.g. https://idealheating.com/tips-and-advice/why-is-my-boiler-losing-pressure
e.g. https://idealheating.com/tips-and-advice/why-is-my-boiler-losing-pressure
@BenAveling Ah thanks, I'll try topping up the pressure.
It behaves the same way with very short cycles when I set the target room and flow temperatures to the maximum.
It behaves the same way with very short cycles when I set the target room and flow temperatures to the maximum.