Airlock in heating system when left to cool down

[stevemof]

Standard old 1980's unpressurised system with open header/exp tank. If the system is left off to cool for even a weekend I get air in the system which seems to stick at the brand new pump, making it noisy and some rads don't heat up. Switching pump on and off a few times makes glug glug noises as the bubbles make their way to the header tank overflow. Once cleared all rads are piping hot.

Where does this air keep coming from?

Would chemicals in system reduce surface tension and prevent it anyway?

Cheers

Steve

 

[HERTS P&D]

Try turning your pump to a lower setting and your system should have inhibitor in it.

Also check your expansion tank has water in it.

Andy

 

[stevemof]

Thanks Andy. I'll let you know about the inhibitor as the tank is always fine and desperate fiddling with pump speed in the past has little obvious effect to date. Steve

 

[HERTS P&D]

They are 'normally' set on speed 2, but try speed 1.

Andy