Air in heat exchanger ?

[Graham Jones]

Hello,

I have a Baxi Barcelona system boiler.

After draining the system down a couple of months ago I am experiencing an annoying problem. The noise of the water being pumped around gets louder and louder, sometimes where pipes are unsecured properly you can hear them vibrating.

I can cure it by isolating the flow and return and draining down the boiler and then topping up. The noise completely goes away, but over time gradually starts to return again.

My guess is that air is trapped at the top of the heat exchanger and by draining down I remove this air somehow! Could this be right?

In the past any air trapped in the system would go to the towel rail in the bathroom (the highest point). But this doesn't happen anymore, it is always OK.

My next idea is to replace the auto vent valve (which is open by the way) and maybe also add some noise reducer.

Any ideas on what is happening here most appreciated,

Thanks,

Graham

[Graham Jones]

Thanks for the reply Harry, there is no speed setting on the pump. By open I meant the black knob is not turned all the way down but is open by one turn. Is this how it should be?

Graham

[A Plumber]

Yes that's correct. The cap is just there if the thing goes faulty and leaks water, you can close it off. There is a float inside that opens a needle valve if air gets into it. They can fill with crud and jam shut. I would start there as the system has worked before. Is this a vented or unvented system? If unvented you could have a faulty pressure vessel. If they go faulty, as the system heats water is forced out of the safety valve. When it cools air is drawn in. (Check pressures, there should be a pressure guage somewhere.)

Suggest you put some inhibiter in, that should quiten it down

[Graham Jones]

Hello Harry, it is an unvented system but the pressure vessel was replaced earlier this year so that is probably OK. I tried to remove the auto vent valve but it seems to be stuck solid, I was too frightened of breaking something to use too much force. Is there anything else I can try?

Thanks,

Graham

[Tabby]

If its vibration, a pump issue or inadequately secured pipes. If its kettling, turning the boiler thermostat down is likely to work.

NT