I had an ASHP fitted last year as part of a hybrid system, which includes a regular gas boiler and a ‘hybrid manager’ which decides whether to burn gas or electricity depending on the outside temp, demand, required room temp and the ratio of gas price to electricity price. So my analysis is somewhat skewed as it’s not just an ASHP running, but could be a regular gas boiler…
Previously I had a system boiler, so had the 2-channel Wiser Hub controller - one channel for heating, one for hot water. As the new hybrid system was using a combi boiler, I had to purchase a new single-channel Wiser Hub, as the 2 channel hub switches mains voltage, whereas the new hybrid manager required a zero-volt switch.
Once the single-channel was connected up, I set the Boiler Type to heat pump, as I assumed that would be the primary source, especially before any harsh winter weather started.
Obviously the ASHP does not reach the same flow temp as the gas boiler, so the heating tends to run longer when using that as the heat source. Another thing I soon noticed was the ramp-up time for the ASHP - it can run for about 30mins before I even start to notice any heat in the first radiator in the circuit. I know the Heat Pump setting on the Wiser system means it should run 20 minute cycles, and I personally find this is too low for my system. To overcome this, I have set the default Boost to 90mins and a +3deg raise, and when the ASHP is used as the heat source, I will use this to ensure the pump runs for a decent time.
I do feel the Wiser system - when left by itself - will start the ASHP running, and then stop it when it’s just starting to produce heat, then start it up again a short time later. It might be the ‘learning’ side of the Wiser system is confused by the response when the gas boiler kicks in, with instantaneous heat and higher flow temps. I spent a lot of time setting different ‘required room temp’ values on the hybrid manager to either force the ASHP too kick in (lower req’d room temp) when generating a lot of solar power, or forcing the gas boiler to kick in (higher req’d room temp) when no solar generation or colder outside temps.
So in summary, I don’t think the Heat Pump setting on the Wiser system really allows the ASHP to run long enough - I think there is too much modulation. But this might not be a Wiser issue - I really wish I had more (remote) control over the Hybrid Manager so I could force it to run and burn gas or electricity based on my own - or HA’s - observations of required temp, solar generation and ambient outside temps.
