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Tim JA
Tim JA, Engineer
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I have a traditional gas fired heating system with a vented

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I have a traditional gas fired heating system with a vented indirect cylinder. I seem to have a leak some where as the f & e tank is constantly dripping and I have had air locks occurring in the above ceiling radiator heating pipes. The confusing point is that the cylinder has two separate 22mm cold feeds one from the [email protected] tank the other from the cold water cistern. What’s the problem
JA: What have you tried so far with the leaky pipes?
Customer: When I drain the FE tank my hws stops flowing despite the feed from the cistern still being open ?
JA: How long has this been going on with your pipes? What have you tried so far?
Customer: I have had regular air locks for the last year .For five years prior none.
JA: Anything else we should know to help you best?
Customer: have you have knowledge of a an indirect cylinder having two 22 mm cold feed connections?

Good morning, and welcome to the Technical section in JustAnswer, an independent paid question and answer platform that matches customers' questions to experts in various skills. My name is ***** ***** I'll be happy to help you today.

An indirect cylinder should have an F&E cold feed entering the primary circuit at some point. Are you saying that you have that, plus a connection to the cylinder from the F&E? Could you attach a photo showing the entire cylinder so that I can see this connection?

Regarding the drip, is the water surface in the F&E higher or lower than that in the cold storage cistern? And does the F&E water level reach the overflow warning pipe outlet?


There's no time pressure on this topic - it will stay open to you for many days, and you can reply at any time. I will be away from my desk sometimes, but will respond as soon as I can.

Customer: replied 15 days ago.
The system is bog standard arrangement , gas fired boiler pump, three way valve, vented indirect cylinder. The oddity is the extra 22 mmm cold feed manufacturers connection on the cylinder being feed from the f e tank there is also a 15 mm cold feed into primary return . Have you come across a standard cylinder with this extra connection ? The heating pipes to radiators are buried in the solid ground probably 40 years ago, this the most obvious causes for a leak! The new boiler and cylinder were installed by British Gas about 10 years ago. I’ve been called away now so I’ll respond to your reply later. Thanks

It might be a vent, but I need to see it.

Please attach two photos that show each end of this 22mm cold feed.

Customer: replied 14 days ago.
I’m using an iPad. It’s difficult to photo. The cylinder connection is a 22 threaded pipe emerging from the cylinder and the feed pipe is a stranded Prestex no. 1 coupling. The fe tank has a standard Prestex tank connector fitted to the side of th tank near the bottom.

From your descriptions you have three cold feeds from the F&E cistern - two are in 22mm pipe and one in 15mm. Is that right?

Regarding the connection between the side of the F&E cistern, low down, and the side of the cylinder. You haven't said how high that connection is on the cylinder, but so far it sounds like a secondary take-off; this is intended for connection to a shower pump, or any installation where you need to eliminate all air from the DHW service.

If that secondary take-off is connected to the F&E cistern, then the secondary water will become polluted with primary water. So, I have to ask the following questions again:

1. Is the water surface in the F&E higher or lower than that in the cold storage cistern?
2. Does the F&E water level reach the overflow warning pipe outlet?

Customer: replied 13 days ago.
Hi Tim I replied to you at 22.45 yesterday. Have you any experience of a cylinder with this extra female connection.

I can see no post from you after my post timed at 22:45. Please can you repeat your answers to my questions?

Customer: replied 13 days ago.
Thanks Tim. The Fe tank has two cold feeds 15mm going into the primary return 22mm going onto a pipe protruding near the base of the cylinder. This cylinder connection is not a site addition. The fe tank is 2ft below the cold storage cistern. The water level never reaches the overflow. This cylinder arrangement is something I’ve never come across and I can’t find one listed in any suppliers list.?

OK. And is there a 22mm cold feed from from the base of the cold storage cistern, also going into a connection near the base of the cylinder?

And you mentioned draining the F&E tank - are you bailing it out, or draining the primary circuit from a drain off sock somewhere?

Customer: replied 13 days ago.
there is a 22 feed from the side of the ',Fe tank to near the base of the cylinder. When I stop the cold water supply via the ball valve to the Fe tank after drawing off a quantity of domestic hot water through showers and taps etc the flow stops when the level of water in the Fe tank falls below the 22 mm conn. to the pipe going to the cylinder.
Customer: replied 13 days ago.
Sorry, yes there is a 22 cold feed from cold water cistern going to a female connection at low level on the cylinder

OK. So if you start using hot water by opening a hot tap, a modest amount (not a trickle and not a torrent), then wait a couple of minutes, then go into the loft and examine both cisterns, which cistern has water flowing into it?

Customer: replied 12 days ago.
Thanks I’ll try that in the morning and report back

Okey dokey.

Customer: replied 12 days ago.
I’ve tried your suggestion drawn off hot water water is refilling into the Fe tank. No sign of the ball valve opening on the main storage cistern

OK, so that shows unequivocally that water from the F&E is entering your secondary water storage.  There are there two possible explanations for that:

1. Someone connected the two without knowing what they were doing;

2. That feed into the cylinder is into a second coil that has perforated and is letting into water into the secondary water.  A second coil in a cylinder, when present, is used for a supplementary heat source such as solar heating or a solid fuel boiler.

3. That F&E cistern is actually a small cold storage cistern.  Naturally this would lead to a question about top-up water for your primary circuit, so it possible that your primary circuit is unvented?

In the case of 1 and 2 above, your potable hot water is compromised, tainted, and hygienic. If 3, then there’s still a mystery to solve.


Everything here is odd, so you were right to be suspicious about it.  One of the many unexplained things  is why no water flows from what you thought is the ‘main’ cold feed from the large storage cistern into the cylinder.

Customer: replied 12 days ago.
The oddity is this is a standard 120lt cylinder with this Extra 22 male connection. The system was installed about 10 years ago ( by British Gas )and the users have never had a problem in use. Until this persistent drip Occurred. Have you ever come across such a cylinder? Are you able to offer any further advice.?

When you say “22 male” I presume you mean 3/4” BSP male?  If not, please attach a photo of it.

How many connections does the cylinder have, in total? Is it branded?

I don’t know why you’re regarding the drip as a problem. If water is regularly leaving the thing that appears to be (but might not be) an F&E cistern then it will be regularly filling.  And if the float valve is worn then it will drip a bit.

One thing that has no explanation at the moment is why no water flows out of the cold storage cistern and into the base of the cylinder.  Is there a valve on that outlet that has been closed?

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