Air being drawn into system after removal of back boiler

[shamrock]

Hi guys

I moved into a bungalow and recently removed the hearth,fireplace and back boiler

The back boiler used 3 tappings

The top tap is the flow to the cylinder
The bottom 2 are the heating flow and return

To give me heat and water I connected the 2 flows but now there is a massive amont of air being drawn into the system - at the start of every day I could bleed the 2 rads first on the system almost completely

I reckon it is coming in through the open vent at the header tank

So

1. am I right

2. Can I put an automatic air vent on the open vent(problem being I don't know if these allow steam out in case anything did ever overheat at the cylinder but it would cure the intake of air surely ?)

Many thanks for any help

[alanka]

No, you cannot put any kind of valve in the safety vent to the header tank -- dangerous and not permitted!

Could air be being drawn in due to a poorly-positioned heating circulating pump? This can create low pressure in the vent pipe and cause air to be sucked into the system. Where in the circuit is the ch pump in relation to the vent, header tank, and boiler? How far below the header tank is the pump situated?

Have you checked that the air is indeed being drawn in via the vent pipe? (Put your finger over the end and see if it is sucking there!) Air can also be drawn in via a leak in the system, if the leak is in a below-atmospheric-pressure part of the pipework.
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Cheers, Big Al