I have an Intergas boiler that supports OpenTherm and currently a 7-day digital thermostat (Honeywell CM67). The thermostat is getting long in the tooth so I'm thinking about replacing it with a T4M which is OpenTherm. I've had a look at the wiring on the control panel and discovered that at present the thermostat is switching 240v.
I did think it was just a matter of moving the two thermostat wires off those terminals and onto the OpenTherm terminals then swapping out the thermostat but a heating engineer (who admitted they weren't a sparky) was sceptical when they saw the wiring. They were of the opinion that because my house is Y-plan what I wanted to do would stop the hot water working. That seems unlikely to me because from what I can read online the hot water will fire the boiler when timer requires it and the cylinder 'stat requires it - with the boiler switching the pump on itself. Surely this is no connection between the thermostat and the hot water otherwise I wouldn't be able to get hot water in the summer when the room 'stat is almost always off.
My only concern is that that the thermostat is sharing the same wiring cable as everything else going to the boiler and there might be a risk of the OpenTherm signals being corrupted because they are in close proximity to mains voltage (seems unlikely given that O/T is 1,000b/s.
Actually as an aside would anyone care to guess what efficiency improvement I might see? I'm assuming not very much because the Intergas is already modulating to an extent but would be curious if anyone has any experience of doing this.
I did think it was just a matter of moving the two thermostat wires off those terminals and onto the OpenTherm terminals then swapping out the thermostat but a heating engineer (who admitted they weren't a sparky) was sceptical when they saw the wiring. They were of the opinion that because my house is Y-plan what I wanted to do would stop the hot water working. That seems unlikely to me because from what I can read online the hot water will fire the boiler when timer requires it and the cylinder 'stat requires it - with the boiler switching the pump on itself. Surely this is no connection between the thermostat and the hot water otherwise I wouldn't be able to get hot water in the summer when the room 'stat is almost always off.
My only concern is that that the thermostat is sharing the same wiring cable as everything else going to the boiler and there might be a risk of the OpenTherm signals being corrupted because they are in close proximity to mains voltage (seems unlikely given that O/T is 1,000b/s.
Actually as an aside would anyone care to guess what efficiency improvement I might see? I'm assuming not very much because the Intergas is already modulating to an extent but would be curious if anyone has any experience of doing this.