![]() ![]() Is this maybe where the valves/thermostats should be connected? In the Viessmann H1 External Extension, there is a connection numbered 143 which in the manual is described as external blocking/external demand. ![]() Surely they should be connected some how? But there seems to be no connection to/from the thermostats/valves. The DHW pump and central heating pump (maybe the DHW recirculating pump too - I'll need to check) are all wired through the Viessmann H1 External Extension which in turn is connected to the boiler using the KM Bus. Normally, do the switches on the valves normally tell the boiler to fire when they are open and in turn the boiler tell the valves to close when the central heating is off? Now I've figured this out I can stop it by turning the thermostats right down to zero when the heating is off, but it's not really practical. So it turns out the odd times of luke warm heating are caused by the central heating valves remaining open when the heating is off, but the DHW is on and in turn pumping round the central heating system. So when the thermostats are turned up and click, the valves open and when the thermostats are turned down and click, the valves close, but they don't seem to tell the boiler this. Now, to me it seems the thermostats don't actually talk to the boiler - from the junction box there is power to the Viessmann H1 External Extension, but no other connections. ![]()
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