Water shooting out of over flow

Hi
Have a old glow worm boiler space saver 38
When run just the water & not rads every so often hear a banging noise & when looking in the loft I can see water shooting out of overflow pipe .
When run rads & water together it is fine ...
Any ideas ?
Cheers Steve

shooting out of overflow pipe

Click to expand...

Do you mean the overflow pipe or the vent pipe?

steveeg said:

Hi
Have a old glow worm boiler space saver 38
When run just the water & not rads every so often hear a banging noise & when looking in the loft I can see water shooting out of overflow pipe .
When run rads & water together it is fine ...
Any ideas ?
Cheers Steve

Click to expand...

sounds like either 1. a faulty pump causing to overheat and blow off or 2. no air in the expansion vessel, no room for expansion of hot water and causing system to rise in pressure and blow off, if its this you will be constantly topping up water pressure in your sytem

second 1 only if a sealed system.....

give more details for better help though..