'British Gas' Ideal RD2 450 Bleeding

[Schmill]

I have a British Gas boiler, which I believe is actually made by Ideal, and is an RD2 450.

A while back I was having circulation problems and noticed that some of the rads were a bit gungy, so I drained down the system and refilled and drained with fresh water a couple of times, (concrete floors downstairs so all rads & boiler are at the bottom of loops, and each has a drain-off point).
Refilled the system with a cleaner and ran for 2 weeks, as instructed, then drained, and refilled with inhibitor.

However, whenever the system starts or stops now I am sure I can hear gurgling from within the boiler as if there is air trapped somewhere. I thought it would work it's way out, but it doesn't seem to have done so, although the water seems to circulate fine.
There was a drain tap fitted to the bottom of the boiler which I used when I was draining and cleaning the system, but as far as I can tell there is no 'bleed valve' or anything similar at the top.

Does anyone know of how to bleed these boilers, or if there is no way, how I can try and shift the trapped air? I have tried running the boiler and pump (set at it's highest speed) just going through the HWC as that is the shortest possible circuit, but it doesn't seem to want to shift

 

[45yearsagasman]

The RD2 450 is a Mexico boiler with fan flued operation.There are no air bleeds fitted to this boiler.If the flow and return pipes are rising from the top of the boiler as you describe then any air should vent automatically to the highest point and then be expelled via open vent pipe or through auto/manual air vents if fitted.I'm assuming your system is standard open vented.

 

[Schmill]

The pipes do rise, but no very far. The boiler is fitted under a kitchen worktop and I think that the supply & return rise out of the boiler, and then run horizontal under the worktop to the opposite wall of the kitchen, before then travelling up alongside the soil stack to the first floor, where they then track round under the bathroom floor, and into the airing cupboard.
Just wondering if it is too far for the air to travel to get 'free'.

Either way, I can here the water / air slosh in the boiler when the pump (in the airing cupboard) starts and stops, so do you have any techniques for removing the trapped air? Would attempting to drain it again and refill help?

 

[45yearsagasman]

Your pipe runs don't sound ideal.If you can get to the back of the boiler you could try and bleed by carefully slowly undoing the flow connection and try venting that way.Failing that try draining and refilling slowly.It may be that the system still has a restriction and is pulling in air.Sorry can't be more specific but give that a go.Maybe others have some ideas?