Domestic central heating circulation

[Manty]

I have a simple system, Thorn Olympic boiler 20 years old, Y valve,single pump,4 bed semi. All worked fine until recently when pump got noisey, i changed it , now after continually bleeding, system fails to circulate when shut down over night, sounds like air in pump, if you turn off and on it works. Noticed of late popping sounds from boiler , could it be getting thin and localised boiling? But why does`t it go straight up the vent?

[pilotlight]

Manty, not too clear re some of your descriptions, but here's a few checks you can undertake : 1. Have you fitted the new pump to pump in the same flow direction as the old one ? 2. Have you set the new pump at the same pump speed as the old one ? ( usually option of 3 speeds ). Did you notice any black coloured liquid in the old pump ? ( this could be a tell-tale sign that the system is " sludged-up ", causing the original pump to fail.) You will need to flush + cleanse the system should this be the case.

There are other possible causes for the problem, I would suggest a call to your local plumber / heating engineer should none of the above work.

Good luck.

[stanleyman]

Could be drawing air in if the pump speed too high or more powerful. A poorly designed system can work just ok for many years then any change can alter the fine balance. Set the pump at lowest speed. You could consider changing to a sealed system to avoid all this. You might also think about a new boiler considering its age and low efficiency. New boilers have to be high efficiency condensing with all proper system controls.