gravity hot water not working, pumped central heating working

[njk]

We have an old boiler (on the ground floor) with a gravity hot water system and 2 pumped central heating circuits. The 2 central heating systems are working fine but we have no hot water and the one radiator on the primary system is not working. This was working when we moved into the house 4 weeks ago.
We had to drain the system last week as we wanted to remove an old and leaky radiator. We removed the radiator and capped off the feed and return pipes. We refilled the system, bled all the radiators and all but one radiator is now working well. The one radiator which is the only one on the primary gravity system is still cold and there is no hot water. None of the pipes in the airing cupboard is warm/hot. There is water in the cold radiator (no air comes from bleeding) so have checked the header tank, which is full, and the upper of the 2 pipes from the hot water cylinder. This also seems to be filled with water.
There doesn't seem to be anywhere else to try to check for air in the system which others seems to suggest might be causing our problem.
The pipes from the boiler are all hot but further up on the other side of the wall there are 2 pipes and both are cold - we assume at least one of these should be hot.
Can anyone suggest if there is anything we can try next? Is this likely to be an airlock or a blockage or something else?

 

[diamondgas]

njk :welcome: to the forum

sounds like an airlock in your gravity system ... could be in either of the two pipes alas

Not an easy one to resolve without some form of experience IMO ... You could try putting your boiler on max hot water only and see if that shifts anything. Failing that I'd suggest you get a professional in..

Plenty on here

 

[marleyco]

Had that problem once when I drained the system.it was the hot water coil I was struggling with. I tried all kinds, in the end I put mains down the feed inside the header tank, which pushed water through the boiler but was still struggling to push it through coil, I put a gate valve on both pipes to boiler so when I put mains water through again it went directly through the coil on hot tank, it solved the problem. It sounds a bit of a task but if you have the gear its not too bad. Mains into tank, so connect there with push fit pipe and put it into feed inside tank, water will come through vent which indicates the water has come full circle

 

[diamondgas]

......... I put a gate valve on both pipes to boiler so when I put mains water through again it went directly through the coil on hot tank, it solved the problem......

I hope you removed them afterwards marleyco??? If you valve off the flow and return pipes from the rest of the system you create a sealed system without an expansion vessel or pressure relief valve!!! Turn the heat on to the boiler on and you've got one heck of a bang!! ... Scary!

 

[tamz]

Bit easier to pull the stat

 

[marleyco]

I hope you removed them afterwards marleyco??? If you valve off the flow and return pipes from the rest of the system you create a sealed system without an expansion vessel or pressure relief valve!!! Turn the heat on to the boiler on and you've got one heck of a bang!! ... Scary!

I know what you mean, I never removed them as I saw it as a future means of helping me if I ever go back and do more work. They can't be closed unless they used tools. And they are left fully open. That was about 2 years ago, so not worried

 

[marleyco]

Bit easier to pull the stat

Your right about that

 

[Js58gas]

I would say tamz has the right idea pull the boiler stat from the heat exchanger and boil up the boiler this will push the water through the gravity circuit. Just remember to put the stat back in.

 

[jtsplumbing]

Try undoing the top connection (flow pipe) on cylinder and just ease it out a little you may clear the air in the coil I have done this in the past to move air locks ! give it a go it may solve your problem.

 

[Puddle]

I would say tamz has the right idea pull the boiler stat from the heat exchanger and boil up the boiler this will push the water through the gravity circuit. Just remember to put the stat back in.

If you do this make sure you let boiler cool down before you put the boiler stat sensor back as if not it can be damaged and end up having to replace it