Air Trapped in Boiler

[S6PNJ]

I'm in the process of renovating (slightly) a house and have had the central heating system drained down to remove a few radiators. Upon refilling and bleeding the system, it sounds like I have air trapped in my boiler - it sounds like you can hear the water trickle in (though I'm sure it's flowing without any problems). It is not a kettling noise as it happens even when the CH pump is running but the boiler is not fired up.

I've bled all of the radiators (which all get hot fairly quickly), the hot water system works fine, I've bled the air valve in the airing cupboard (little thumb valve?) and also the pump has been bled (screw in the middle).

The boiler is an Ideal Classic RS40 and apart from the (slight) noise I can hear of the water trickling in, everything else appears to be fine. With the covers off the boiler there isn't any bleed valve I can see in the water jacket and the feed and return pipes are vertical to/from the boiler.

The boiler is in the kitchen (ground floor) and the hot water tank is upstairs. The header tank in the loft is full and flows fine (sorted the blockage out that was in the cold water feed pipe).

The heating has been on for the past week and the noise hasn't gone - I've been checking all bleed valves regularly to make sure all possible air is gone.

Any clues as to what to try next?

[S6PNJ]

Arthur Jackson said:

Have you tried it on hot water only with any bypasses shut and the pump up full? It sounds like the pipework above the boiler might be trapping a little air.

I've tried it all ways! Yes, hot water only, pump was set to full by default (I II or III - Standard Danfos(?) pump). I'm sure it is air trapped, it's just trying to get it freed. The pipes go up into the bathroom then run horizontally to the airing cupboard where the pump and remainder of the pipework is (3 way valve, cold fill, air bleed of the gravity fed hot water tank). When the pump switches in, you can hear the water initially rushing through the pipes - just got to get it out!

[S6PNJ]

dirkgently said:

looking at the boiler the tappings go:
Gravity flow (capped)
pumped return
Gravity return (capped)
pumped flow

Just check that the pumped flow is getting hot before the pumped return.

Yup, that's what I've got on top of the boiler (well, I've got GF PR GR and PF which I worked out to be what you wrote!) and the flow is getting hot before the return - no problems there.