![]() ![]() The probable reason it isn't is because the pipework on this section is. I'll put up a diagram to better explain this.Īlso, the boiler is weather compensated, which might shed some light on things.Īnyway, on this initial central heating loop there is a gate valve which I believe would preferably/normally be an automatic bypass valve. If in the course of that hour I were to turn the the thermostats right down so they click and the motorised valves close, the central heating pump would continue to run and the hot water would simply trundle round the initial first loop of the central heating pipework - as in the loop before the three zones flow and return pipework tees off of and onto. For example, set a heating period from 7pm to 8pm, the boiler comes on for that hour regardless of what the room temperature is or if the valves are closed. Heating times are set on the boiler itself. ![]() Hi sircerebus666 and thanks for the reply. Obviously all this depends on readers knowing a bit about Viessmann boilers and components, but any advice would be very greatly received. 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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