i have a Valiant combination boiler and no means of water storage.
Recently i noticed something odd. Once i run the hot taps (particularly in the bathroom) for a period of time and then turn them off the towel rail starts to gurgle almost as if there is air in the system.
Also once the towel rail does its gurgling noise the boiler will partially fire as if its getting a back feed.
i am confused as to why this is happening as i thought the hotwater and the heating were two completely different systems.
Also something else which struck me as odd is that if the hot tap is left on i.e. running a bath the pipe which enters the bottom of the towel rail gets hot but only on one side. the rail itself stays cold except the very bottom which starts to warm.
I have kept an eye on the pressure gauge in the boiler and this doesnt change and is constant at around 1 bar.
The heating and hot water are different circuits, but are in a way connected. The boiler heats the water in the primary circuit which in turn either circulates through the radiators OR through a second heat exchanger to heat the hot water.
Maybe what you are seeing is "pump over run" which happens after the call for heat has ceased and the boiler has shut down. Residual heat in the main exchanger continues to heat the primary water to the point it may boil so to prevent this the pump continues for a short time dumping the energy into the radiators.
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