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Air Trapped in Boiler

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S6PNJ

Original Poster:

2,379 posts

188 months

Wednesday 26th October 2011
quotequote all
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?

dirkgently

1,907 posts

138 months

Wednesday 26th October 2011
quotequote all
The only time that I have come across that the flow and return had been reversed during installation,changing them over solved the problem.

Arthur Jackson

2,111 posts

137 months

Wednesday 26th October 2011
quotequote all
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.

S6PNJ

Original Poster:

2,379 posts

188 months

Wednesday 26th October 2011
quotequote all
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!

Deva Link

26,934 posts

152 months

Wednesday 26th October 2011
quotequote all
Does the water level in the header tank rise significantly when the pump is turned on?
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Arthur Jackson

2,111 posts

137 months

Wednesday 26th October 2011
quotequote all
S6PNJ said:
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!
It can only be trapped at a high point. You could stick a hose on a drain-off and blast it backwards, but take care.

Deva Link

26,934 posts

152 months

Wednesday 26th October 2011
quotequote all
hora said:
I don't know if this helps but we had wierd 'tung!' Etc noises when boiler running. Found out it wasn't the rads but the water pressure too high running into/through the boiler.

My fix was simply to turn down the stop tap (the water coming out of the taps was silly fast)
That's for a combi - the OP has a regular boiler.

dirkgently

1,907 posts

138 months

Wednesday 26th October 2011
quotequote all
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.

S6PNJ

Original Poster:

2,379 posts

188 months

Wednesday 26th October 2011
quotequote all
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.

fatboy b

7,131 posts

123 months

Thursday 27th October 2011
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Having read the title, the first thing I thought of was "Can't she fart it out?".