Hive heating & hot water install wiring help with existing CH thermostat

[ChrisGG]

I was going to add, with each of the combinbations can you see which zone valve is open and perhaps if you can feel a flow through the pipe.

Does the boiler stop when the HW boost ends?

If the CH zone valve is faulty I would expet the problem to occur during central heating only cycles as well.

If you look at the JW video I linked, around 11:40 in he explains the CH function. As you will see there is no direct link between the programmer and boiler. The programmer activates the zone valve, that closes a switch which starts the boiler. So if the microswitch "sticks" closed the CH circuit will run independent of the programmer.

And yes, the likes of Hive & Wiser run the system more frequently. Traditional systems with mechanical thermostats had a fairly wide hysteresis which just means there was a large margin between the off and coming back on. For example if the stat was set at 20C, it would turn off at 21C and not turn back on until 19C or something like that due to the design of the stat. An electronic stat has no moving parts and hence the Hub can run to a much tigher tolerance. On my Wiser system it's around +/- 0.3 C. It did worry me initially as I was used to a boiler that worked in long on/off cycles and the boiler now performs up to 6 complete on/off cycles per hour. Often the boiler may only run for a couple of minutes as the system attempts to maintain a steady temp.

Appreciate the detailed response and background to the differences in old versus new thermostats. Makes sense. I'll do some more investigation on the valves the next time the issue occurs and see if I can feel a flow. Thanks again.

 

[ChrisGG]

Just to update: British Gas Engineer confirmed the CH 2 port Myson zone valve had developed a faulty microswitch. Replaced with a brand new Drayton 2 port valve and actuator. I guess the frequency of the Hive maintaining CH temp running the heating more frequently for sorter bursts was too much for the old valve. Anyway all fixed. Nothing wrong with the Hive or my wiring!