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Bungalow with old microbore system running a new Worcester gas boiler. Central heating works fine until hot water is turned on then there is a massive gurgling sound and I have to bleed several rads. The system is indirect with new rads & TRVs. My thoughts are the level in the primary vent pipe is being drawn down sufficiently to let air in. The present vent is connected into the 28mm pipe between the boiler flow and the pump input (close to the pump) but at a level only about 1.5 metres below top of vent pipe.

Could this be the problem?

Sounds quite a reasonable explanation of your problem. To prove the point put your thumb over the vent pipe as the water is turned on and see if it is sucking.

As a matter of point, on a well designed system, the primary filling feed and the expansion pipe should connect to the circuit no further apart than 150mm to prevent air intake or over pumping. The further apart they are then the greater the chance of a problem occuring.

Irrespective of the problem your symptom is something the installer of your new boiler and radiators needs to address.

Get him back in and don't fiddle with anything until he has been. That way he can't avoid any responsbility by saying " nothing I can do - someone has been playing about with it".

Cheers

Make sure the AAV is open on top of boiler.

[quote="plumbbob"]Sounds quite a reasonable explanation of your problem. To prove the point put your thumb over the vent pipe as the water is turned on and see if it is sucking.

As a matter of point, on a well designed system, the primary filling feed and the expansion pipe should connect to the circuit no further apart than 150mm to prevent air intake or over pumping. The further apart they are then the greater the chance of a problem occuring.[/quote]

Thanks for that I will check it

Hello!

You've just had a new boiler and radiators fitted. The system ain't performing by all accounts! Get the installer back to fix it!!!!!!!