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iansas · Joined: 27 Dec 2003 Posts: 40 Location: brook surrey uk

can anyone help?
mysystem has been fine for 3 years but now the boiler has started banging which i imagine can only be air in the system. i drain it down and it is fine for 2/3 weeks until it starts baning again, i have 2 auto airvents one before the pump and one before the cylinder (hot water). the cold fill is on the return just before the pump, the safety vent is on the hot water return just after the cylinder. (i think its drawing air in the safety vent). the pump doesnt like the no 3 setting it makes alot of rushing sounds. the pump is in a short run and its busy pipework. the boiler is a camray compact 50/70 oil fired and it heats up very well except the anoying banging noise it is in the garage with long pipe runs in 28mm.

AlanE · Posted: Sat Dec 27, 2003 7:55 pm Post subject:

There are two types of automatic air vents. A bottle type which contains a small quantity of water and a float. The other consists of a bolt and fibre washer. What type have you got?

Alan

iansas · Joined: 27 Dec 2003 Posts: 40 Location: brook surrey uk

[quote="AlanE"]There are two types of automatic air vents. A bottle type which contains a small quantity of water and a float. The other consists of a bolt and fibre washer. What type have you got?

Alan[/quote]they are both folt types and both just replaced

AlanE · Posted: Sat Dec 27, 2003 8:10 pm Post subject:

Did you mean the bolt type? If so loosen them with the pump stopped and let the air outand water should flow. Then tighten them. Then try rerunning the system.

Are the fitted at the top of a short length of pipe?

Do you have motorised valves and were they manually opened when the system was filled.

Alan

iansas · Joined: 27 Dec 2003 Posts: 40 Location: brook surrey uk

they are self venting float types, yes one is in a small section to the cylinder 300mm and the other is in a rising pipe about 400mm long just before the pump (200 mm) . i did open the 3 port valve manually for filling.(thanks for quick reply alan )

ChrisR · Posted: Sat Dec 27, 2003 9:01 pm Post subject:

PIpe layput is not ideal. Avoid sucking air down the vent (check by holding glass of water up under it) even if that means turning the pump down.

iansas · Joined: 27 Dec 2003 Posts: 40 Location: brook surrey uk

thanks chrisR, i have fitted a check valve to the vent pipe but didn't check to see if it pulls before doing that.

AlanE · Posted: Sat Dec 27, 2003 9:13 pm Post subject:

Have I misunderstood but you say the vent is on the cylinder return (after the pump) and the cold feed is on the input to the pump.

The only way the pump can suck air if it has been removed and put in the wrong way round.

The vent pipe should be a continuation of the upper connection from the boiler and run in an upward direction all the way to tank.

If you have the bottle type air vents they are supplied with plastic caps. Did you tighten them again after refilling the system?

Any possibility of a diagram or digital picture?

Alan

iansas · Joined: 27 Dec 2003 Posts: 40 Location: brook surrey uk

yes the vent is on the bottom(return pipe) from the hot water cylinder not in a continual rising pipe from the boiler as the boiler is 6meters away in the garage.
i think you are right Alan !! i will draw a picture and email it to you. give me 10 mins.

iansas · Joined: 27 Dec 2003 Posts: 40 Location: brook surrey uk

i have mailed a diagram i hope it helps.
i think the cold fill and the safety vent could be changed in the loft giving the vent pipe a direct rise from the boiler flow and the cold fill would definatlely benifit from being in the return. but i just can't see how the air gets in or was in when i filled it up.

thescruff · Moderator Joined: 03 May 2003 Posts: 4680 Location: Bath

REMOVE the check valve Immediately before you blow your self up, DO NOT USE THE BOILER

Evil or Very Mad

email a drawing to scruff2@ blueyonder.co.uk

AlanE · Posted: Sun Dec 28, 2003 9:11 am Post subject:

Just looked at drawing and would repeat thescruffs comment REMOVE the checkvalve. Whatever made you fit it????

I just reread your posts and noticed you mentioned it in reply to chris's. I missed that thinking it was just a reply to his comments.

The whole system is upside down!!! The vent should be connected where the left hand air vent is and the cold feed then connects within 150mm of this pipe between it and the pump.

The returns from heating circuit are also incorrect. The returns from upstairs and down must be joined before the junction with the hot water return otherwise there is the risc of reverse circulation.

Did the system ever work correctly in its present configeration? Even in the years gone by when it was general pratice for the cold feed to be located at the lower boiler connection the vent ALWAYS went from the top one.

Lastly the top screw of bottle type vent valves should be left loose otherwise any air collecting in them can,t get out thus negating their inclusion.

Alan

iansas · Joined: 27 Dec 2003 Posts: 40 Location: brook surrey uk

thanks all for info especially alanand thescruff for probably saving my boiler and my life !!!!
i am just taking the check valve off the vent pipe (i was told to do it by local plumbing shop, they said it will let out but not draw air in)wont go there again.
just looked under floor boards and upstairs and down stairs heating circuits do join together before they join boiler return.
i will replace vent and cold fill as per your advice alan (thanks again)
the air vents have small holes in the cap with small valves to stop air being pulled into the system, the paperwork with them said to tighten them back up once refilled.
after your help, alan, and all, do you think it will sort out the bang / air in the system?
to be continued !!!!
Very Happy

iansas · Joined: 27 Dec 2003 Posts: 40 Location: brook surrey uk

thescruff i have just mailed you a drawing for your delight!!!

thescruff · Moderator Joined: 03 May 2003 Posts: 4680 Location: Bath

For others that read this disaster waiting to happen.

The vent will allow the system to breath, expanded water has to go back when cooled again, therefore if you take out water and don't allow it back again you end up with a vacuum.
most modern boilers have a low pressure switch which will cut the boiler off.
With a cylinder the vacuum can implode the cylinder when you draw hot water.

scruff