Radiator heats up when hot water is on and heating is off

Discussion in 'Plumbers' Talk' started by AndrewLivingstone, Aug 26, 2021.

  1. AndrewLivingstone

    AndrewLivingstone New Member

    I've a weird issue. I've old vented cylinder boiler. One of the radiator, nearest to the cylinder, heats up when only hot water is on, heating is off. Not sure why only one radiator is heating why not all of them heat up? I got the 3 port valve and pump replaced but problem persists. I'm not sure what else could be the issue. Any thoughts?
  2. ramseyman

    ramseyman Screwfix Select

    That radiator is on the hot water circuit, often done so you can dry things in the summer, usually in a bathroom. Can also be left as a by-pass in older systems
  3. AndrewLivingstone

    AndrewLivingstone New Member

    Thanks for replying. That’s exactly what I thought but my plumber pointed to faulty valve and replaced it. That one radiator comes to action as soon as I turn on water heater so that confirm what you just said. There is another thing that pipe which goes out from valve to radiators heats up when only water is turn on which was the issue pointed out by plumber saying it shouldn’t be hot. Another issue I see is that whole area surrounding the boiler gets very hot pipes are extremely hot. Not sure if this points to anything else.
  4. kiaora

    kiaora Screwfix Select

    Back in the day, when home heating system first started, it was mostly coal fires, a back boiler and a gravity system to heat a hot water tank.
    With no control on the coal fire, the hot water often would get very hot, so a radiator was connected to the gravity circuit, this acted as a heat sink. And warmed the bathroom.
    The next development was to add some radiators and a pump, so when the fire was going really well you could switch the pump on !

    I could go on………
    Bottom line, some plumbers still add the heat sink to the hot water side,

    good luck

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