Domestic hot water not very hot

[deldol]

Thanks, Tamz. I'll have a look at the pipe set up, though I don't know why it suddenly developed this problem a few weeks ago after working fine for at least the last 6 months. I'm definitely getting poor flow through the coil, though - after the boiler being on for 90 mins this morning the bottom half of the cylinder and the return pipe from the coil are both still cool. I will probably put a new cylinder in and make sure there are no run ups in the pipework. Not directly related to the suspected air lock problem, but do you think it's worth changing my Glow Worm to a modern condensing boiler as well (although I realise this is no longer a DIY job)?

 

[doitall]

Yes, the ball valve opens fine.

Did you drain a few gallons of water out to test the ballvalve.

You didn't answer the question.

The most common cause of an open vented cylinder getting air locks in the primary circuit is a blocked cold feed.

Should you decide on a new cylinder, Unnecessarily in my opinion at this time, do make sure you get one suitable for gravity cirulation.

 

[deldol]

Just got in from work and back on the job (the hot water problem, that is).

Sorry, doitall, for not answering your question properly - I thought you were asking it in order to test the ball valve. Anyway, I've now drained nearly 3 gallons (a builder's bucket full) out from a draincock at the bottom of the CH system. I tied the ballcock up first to make sure the header tank was emptying, which it did at the same rate as it was flowing out into the bucket at the other end. I stopped it just before the water level reached the bottom of the tank as I didn't want to introduce more air into the system, if that is indeed the problem. Untied the ballcock, and the tank filled up fine.

So - it doesn't appear to be a blocked cold feed from the header tank.

In answer to Tamz's question - the vent pipe is tee'd off from the flow pipe about 6 inches before it enters the cylinder and the flow pipe appears to be horizontal between the tee and the cylinder. The flow then runs down through the coil and the feed from the header tank is tee'd in just after the return pipe leaves the cylinder.

Must admit that I'm now completely baffled as everything appears to be as it should be. I'm extremely grateful for the very helpful advice from you guys, but so far it seems to have eliminated the possible causes you have highlighted. Anything else it might be?

 

[JohnD]

have a look at where the primary pipe (28mm) enters the cylinder at the coil connection. On the return pipe, is there just an elbow, or is there some sort of valve? You might have a Cyltrol or other thermostatic control; which restricts the water flow when it gets up to temp. They can seize, and they have the wrong effect if hot water goes up the return intead of the flow (can happen with long horizontal runs)

 

[doitall]

I actually meant to leave the water running in, as it can move any air thats trapped.

Can you post a pic showing the cylinder connections and surrounding pipework.

 

[cmother1]

If you want to kick the airlock theory into touch and you like living dangerously.....
Let the system go cold and gently slacken off the connector on the top of the coil. With luck you'll hear a hiss as some trapped air escapes. Have plenty of old towels handy to catch the drips, squirts, etc.
Retighten connector & hope it holds water.

This advice is given without any express or implied warranties

 

[JohnD]

hope

 

[tamz]

Depending on the way it is piped, see if you can lift the flow pipe slightly and jamb something under it.
Could be the coil inside the cylinder has a slight rise.
There is another way to get the air out but i can't tell you for your own safety.....sorry

 

[gassafeman]

Air.

If you can 'boil' the H/W primary's, you will shift it easily.I would suggest you get a decent plumber in to do it, unless your confident enough.

I adopted this approach when a fellow plumber had run out of ideas on a system he was called into repair for the same problem.

Was quite annoyed when he phoned to thank me and explained the customer had better hot water delivery in the last week after living in the house for 7 years. A tenner would have been nice!

Suppose Ill be lambasted for this.... but it works. A cold feed blockage must be ruled out first - quite rare on gravity h/w.

Tamz: Have I said it... sorry.

Paul

 

[tamz]

I tied the ballcock up first to make sure the header tank was emptying, which it did at the same rate as it was flowing out into the bucket

I would think the feed is clear enough.

 

[gassafeman]

Thanks for highlighting that.

Paul

 

[tamz]

Had to do that with 90% of solid fuel back boilers i changed - 100's of them, 3 a week for about 2 1/2 years until i got fed up spitting out soot.

Wasn't a problem with the coal it just kept heating until it boiled it out.

 

[deldol]

Thanks again for all the helpful suggestions (just realised I keep saying chaps but for all I know you could be chapesses).

Got the gist of the suggestion whispered quietly by Tamz and loudly by Gassafeman. Can't do anything until Saturday as I'm out for rest of today and anyway I'll have to choose a time when the other half is out as I think she might be paniced by all those snap, crackles, pops and gurgles.

I've previously had a suggestion of connecting a hose to the draincock on the CH system and turning mains water pressure on. Alternatively just insert a hose through the header tank into the feed pipe and turn mains water on. Worth trying those first?

What about cmother1's suggestion of loosening off the joint on the top of the coil?

 

[tamz]

I know you could be chapesses

With forearms like popeye

Don't bother with the hose the other way will work no problem.

I'll have to choose a time when the other half is out as I think she might be paniced by all those snap, crackles, pops and gurgles.

Sounds more like the pipes trying to jump off the wall.
Don't do it for too long, a few seconds is all it will need.

 

[tamz]

Keep heating off just hot water on.