DIY Doctor

Main navigation

Hot Water venting into the Expansion Tank

Postby slicedbread » Thu Dec 11, 2008 8:37 pm

I'm getting very little heat in the radiators in the system bar the first two. It's never been brilliant but now worse than ever.

I'm also getting a lovely warm expansion tank as the hot water is venting through the expansion pipe and back down the cold feed.

So having turned down the thermostat on the boiler and reduced the flow on pump to one so we don't make the tank too hot.

I've had plumber look at it and he's pointed out that expansion pipe is too small (15mm same as the cold feed)

His suggestion is to turn the system into a sealed system - few days work approx £800

Looking at the forums here I see the advice is often that the expansion is too far from the cold feed. That woul look to be case here as the cold feed is between the boiler and the pump. Not the fogiest where the expansion pipe has come from poss. just of flow upstairs as I can't find it near the boiler and I can't see a 15mm near hot water tank.

So on to the question is turning it into a sealed system likely to be a good suggestion or would sorting out new properly sized expansion lilkly to be better /cheaper?
Rank: Labourer
Progress to next rank:
Posts: 1
Joined: Thu Dec 11, 2008 8:26 pm


Simply Build It

Postby stoneyboy » Fri Dec 12, 2008 10:08 pm

I cannot recall ever coming across a central heating expansion pipe in anything other that 15mm. Your expansion pipe should be an inverted U and I would suggest you try raising the height of the top of the U so that the system can operated at a higher pressure without water being pumped out of the pipe.
Rank: Project Manager
Posts: 4752
Joined: Wed Dec 10, 2008 6:44 pm

Postby plumbbob » Sat Dec 13, 2008 2:12 pm

Sorry Stoneboy, but all expansion pipes must be the same size as the system flow and return pipes which generally are either 22mm for fully pumped or 28mm for gravity fed systems.

Frankly, if you have 800 quid to spare, put it towards a new combi boiler rather than modifying the existing system especially if your boiler is not the condensing type. If you don't, then move the f & E pipes, flush the system whilst empty and when refilled, increase the pump speed to max and balance the system. Will very probably solve the problem.

Oh, and make sure the cylinder has a lockshield valve fitted and make sure any bypass valve if fitted is set properly.
Rank: Project Manager
Posts: 1891
Joined: Wed May 07, 2008 9:59 pm

Display posts from previous
Sort by
Order by

  • DIY How to Project Guides
  • DIY how to tutorial projects and guides - Did you know we have a DIY Projects section? Well, if no, then we certainly do! Within this area of our site have literally hundreds of how-to guides and tutorials that cover a huge range of home improvement tasks. Each page also comes with pictures and a video to make completing those jobs even easier!

  • Related Topics