[MattB]

The boiler has a built in bypass. We keep one small radiator open "just in case" but it cant call for heat. The house is 10 years old and very warm and well insulated. We barely need to heat it even in cold weather.

[Plantagenet]

@MattB
your best course of action would be to get someone competent in fault finding with a voltage tester / multimeter to get to the bottom of it for you.If its electrical then it needs the correct safety checks Carrying out on this before working on it.

[MattB]

Agree and thanks for your expert advice. I find it interesting in that it was not until I could monitor with a smart meter that I realised there was a problem.

[Plantagenet]

@MattB
your towel rails could well be piped to the htg flow and return from boiler before the motorised valves.,whenever there is a boiler demand.

[meldrewreborn]

Just to explain in plain English, when a thermostat calls for heat a live feed goes to the motorised valve, the synchron motor opens the valve and then trips a micro switch sending a different live feed to the pump and boiler. When the demand for heat ceases power to the synchron motor ceases and the valve closes under a spring return. The micro switch will be released and the feed to pump and boiler will cease too.

but if the micro switch contacts have fused shut due to sparking over time then the boiler will still be powered together with the pump. With all 3 valves shut the boiler will fire, get to temperature and shut down, water will circulate though the by pass units, and gradually cool the return flow back to the boiler, where eventually the boiler will fire again and the cycle will then happen again and again.

this would explain the constant gas use from midnight onwards, but not the peak at 03:00.

Posted just for the lay forum members to aid understanding.

[MattB]

Originally Posted by retrotecchie

@MattB
Try putting the heating side on 'timed' and switch off a 'window' between midnight and 7am. See what happens then

Sorry...it's clearly something your Tado system is not doing properly, or you do have some electrical issues somewhere. If you manually turn the boiler off....no gas consumption.

Previously when I turned all the Tado stats to 'off' the same thing happened, so I do not believe it is the tado system that is faulty. You could argue they are calling for heat when not registering that they are, but I do not believe that to be the case.

Thanks again all for your input.

[MattB]

Originally Posted by Plantagenet

@MattB
your towel rails could well be piped to the htg primarys before the motorised valves.,htg whenever there is a boiler demand.

Not sure i understand heating primarys

[MattB]

Originally Posted by meldrewreborn

Just to explain in plain English, when a thermostat calls for heat a live feed goes to the motorised valve, the synchron motor opens the valve and then trips a micro switch sending a different live feed to the pump and boiler. When the demand for heat ceases power to the synchron motor ceases and the valve closes under a spring return. The micro switch will be released and the feed to pump and boiler will cease too.

but if the micro switch contacts have fused shut due to sparking over time then the boiler will still be powered together with the pump. With all 3 valves shut the boiler will fire, get to temperature and shut down, water will circulate though the by pass units, and gradually cool the return flow back to the boiler, where eventually the boiler will fire again and the cycle will then happen again and again.

this would explain the constant gas use from midnight onwards, but not the peak at 03:00.

Posted just for the lay forum members to aid understanding.

Thanks that is hugely explanatory.

[meldrewreborn]

@MattB

the pipes from the boiler before they get to the motorised vales. If towel rails and bypass are plumbed into these they will be hot if any of the 3 motorised valves are open, or indeed if one of the valve micro switches is continuously live.

[MattB]

Thanks.

The graph I posted was intended to demonstrate the gap during the day when I switched the boiler off. Last night was very cold and in fact the tado kicked in on two rooms around 3 am because it got below the 17 degree limit so that explains the peak. But all the hours before that were again not called for by the stats.