Does my theory make sense?

I have a combi boiler and usually have it on and off (timed ) during cold periods. Back in march this year, I tried keeping the boiler on, but turning off the individual radiators around the house. I even studied the gas meter as I did this and when the boiler was ON and all the radiators were OFF, the meter didn't budge. It seemed as though it was OFF. So, does anyone know if this is more or equally as economical to leave the boiler permanently ON during the winter and just turn on/off individual radiators. I.e. I would turn them all off while out at work all day and at night and vary them when I'm home. Hope this makes sense!


  • Unless your boiler is fully modulating whilst in central heating mode, when it is lit will use the same amount of gas for the period it's running no matter how many radiators are open. It probably has an in-built automatic by-pass which means the boiler will 'cycle' on and off all the time that it is in demand mode for central heating. Even if the gas valve does modulate in heating mode, it will still have a minimum heat input of a substantial KW rating.

    Also, unless your radiator valves are thermostatic, the constant turning on and off will cause them to weep out of the top through the packing nut. Assuming they are quality valves that can be repaired, but cheap ones can't be re-packed.

    The most economical way to run the heating is with the timer set to timed programmes when heating is required, in conjunction with a room thermostat and thermostatic valves fitted to the radiators, except the one closest to the room stat. The temperature difference between the inlet and outlet pipes (flow and return) should be twenty degrees on a system with a condensing boiler (60-40), and at least ten degrees on older systems. Balancing a system this way is quite tricky and usually a job for a pro.

    The boiler 'cycling' on and off around it's own by-pass all day is not economical at all.
  • shannishanni Forumite
    353 Posts
    Thanks MSP...I thought my idea might be too easy a solution.

    cheers for the info
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