On Sunday, 13 May 2018 14:47:27 UTC+1, Roger Mills wrote:
On 13/05/2018 09:35, alan_m wrote:
On 12/05/2018 21:37, Roger Mills wrote:

I'm almost tempted to suggest converting the primary circuit to
unvented, which should make it easier to eliminate the air. But it's
worked ok as a vented system for decades - so shouldn't be necessary.

Am I missing anything obvious?

Are all the radiators getting hot? If not you may have a airlock in the
pipes supplying them which may be the source of the some air getting
back to the to the pump or boiler. If so run the pump at full speed and
just turn on one radiator at a time to try and force the water through
the problem pipe length.

Since the tank ran dry have the radiators been bled? While the tank was
dry air could have been sucked in and distributed to the radiators.


Don't forget that there are two circuits, each with its own pump.
Currently, I'm only running the HW circuit - so the rads are cold. But I
*did* run the CH and bled the rads (very little air came out) when I
first became involved.

I omitted to say that there is a towel rail in the bathroom which is on
the HW circuit, connected in parallel with the coil. *That* does collect
air and needs frequent bleeding.
--
Cheers,
Roger
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So just to be sure.... With the current setup, the heating is off and therefore the pump is off. When the hot water pump is off all is quiet and when the hot water pump is on you get all the noises?

You mentioned that the F&E tank is connected to the hot water circuit but assume it must also feed the heating one too? If not, do you have a separate F&E tank for the heating circuit? Finally, are the 2 circuits isolated from each other e.g. via a motorised valve? Wondering whether the water circuit could be pulling air from the heating circuit.