Domestic hot water not very hot

[deldol]

I have a conventional open vented pumped CH and gravity circulation indirect DHW system. Lately the hot water has been taking longer to get warm and seldom gets really hot in quantity, although I have turned up the boiler thermostat. The flow pipe from the boiler to the cylinder is really hot but the return pipe is only lukewarm at best. I did have a problem with an air lock in the coil last year after I had drained the CH system, but that did eventually clear and up to now I have not had further problems. I do not think the current problem is an air lock and may well be a furred up coil, but I did put inhibitor in the system when I filled up. Any further ideas? Am I best just replacing the cylinder - it is probably about 50 years old and it will only cost about £180 incl new immersion to replace.

Thanks in advance for any advice.

 

[doitall]

Have you checked the header tank has water init.

 

[deldol]

Doitall - thanks for reply.

Yes there is water in the header tank and I've just checked that the ball valve is working OK.

 

[kevplumb]

my money is on an airlock again

 

[cmother1]

Do you have a bleed valve near the top connection to the coil? If not the airlock is favourite. Limescale is more likely to form on the outside of the coil, not the interior.

 

[RigidRaider]

Out of interest, what were the symptoms of the airlocked coil? I believe we may have the same.

 

[deldol]

No, I don't have a bleed valve. Last time I had an air lock I didn't get any flow at all and the water in the cylinder remained completely cold. I'm definitely getting some flow now as the water is heating up, albeit more slowly than it should. Can you get a partial air lock? I would have thought it would eventually dissolve and/or dissipate up the vent pipe, but this has been going on for several weeks. If it is a partial air lock, any ideas for getting rid of it?

 

[kevplumb]

what boiler you got ??

 

[deldol]

The boiler's a Glow Worm Space Saver 45-60. Yes, it's pretty old (about 25 years) but dead reliable, I clean it out every year and inspect the burner which is always as clean as whistle. I don't think it's a boiler problem - as I said the flow pipe between the boiler and cylinder is very hot. I haven't had the CH on for ages but at the last count it was working fine.

 

[doitall]

Drain some water out of a radiator, does the ball valve run in the header tank.

 

[deldol]

Yes, the ball valve opens fine.

 

[doitall]

Yes, the ball valve opens fine.

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

 

[Agile]

When you have done that just turn the heating on for a few minutes in case that has any effect on the suspected airlock?

Tony

 

[tamz]

It is a partial air lock. You have some air trapped in the flow pipe somewhere which is restricting the flow.
The pipes connecting to the coil may have a slightly run up ( even 10mm will make a difference as that is 10mm of the pipe without water in it ) which will severely reduce the gravity circulation. The tee for the open vent on the flow should be the high point and it should fall from there through the coil to the boiler.
If you are planning to keep your existing setup changing the cylinder will give a better heat transfer. New cylinders have much better coils.

 

[tamz]

turn the heating on for a few minutes in case that has any effect on the suspected airlock