No Hot Water in Tank

15 Nov 2008
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United Kingdom
Boiler works fine Central Heating and Rads working as they should.

Pipe up to the coil in the hot water tank is hot but cold on the return out.
I have worked out there is probably air in the coil stopping the flow but how do I bleed it.
Boiler is in the basement Hot water tank is on the second floor below its cold fill tank. Above that in the loft space is a small header tank I assume for the CH.

Problem occurred midweek when I cut a radiator supply side pipe when trying to lift a floorboard. Sorted that problem out and got the pipe re-attached and bled the rads through everything on the heating side worked fine. Just ever since there has been no hot water. Lost quite a bit of water and was only able to stop the flow by turning off the main stopcock. It was the very handy availability of a bit of hose and a close by toilet that stopped major water damage but essentially the whole system to this first floor rad drained off.

Should add I have followed the pipes on from the boiler above the hot tank and cold fill tank to where they meet the header tank expecting to find a bleed valve but there is nothing.

I am missing something obvious here and clearly it is a very simple job to bleed to air lock if only I can find out where.

Thanks for any considered replies.
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I would say Gravity HW Down and pumped CH although of course the same pump pushes the hot water up to the tank to heat the coil.

The pump is in the same cupboard as the boiler which is in the basement, there are no others. Whole system is circa 1980 and the boiler is a Glowworm 85-100.
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I would say Gravity HW Down and pumped CH although of course the same pump pushes the hot water up to the tank to heat the coil.

Not quite sure what you mean there... Its likely to be either 'fully pumped' where the flow splits after the pump either by way of a 3 port valve or 2x2 port valves to feed CH and HW circuits, or gravity HW, where the HW circuit relies on gravity circulation from the boiler, using 28mm pipes, (no pump), and the CH alone is pumped.

Do you have anything like shown in the pic Kev posted?
There is a boxed switch of some description just after the pump. When I switch on the CH the switch operates and the pipe run after it gets hot.
Ok, sounds like the motorised valve on the CH circuit, which I believe is working ok from your original post. Is there another of these 'boxes' you can see, or does the pipework Tee off after the pump but before the Motorised valve?? If you could post a pic of your setup it would help us understand the layout of your system a bit better.
Thanks. When the pipe reaches the cylinder does it go straight in, or is there any other pipes coming off it? If you could do a pic of the cylinder showing pipework arrangement on primary side that would be great.
Superb, thankyou. The pipe rising from the cylinder primary flow to above the tank is a vent, this should allow the air to escape as the system is refilled, therefore no need for a bleed valve. I would think there may be a blockage in the return at the bottom of the cylinder, stopping the circulation through the coil. The pipe gets hot as far as the cylinder, could you switch the heating off and see if water is emerging from the vent over the feed and expansion (smaller) cistern in the loft.
I was up there earlier this afternoon and there was no water flowing into it. I did trace one of the upwards pipes which acted as a vent hung over the tank like an overflow.
The heating may have been on at the time though? Wouldn't this need to be the case for the pump to pump water up to the expansion?
I felt for the level of water and it was most definitely cold. I also tested the action of the ballcock which was fine.

There is nothing to suggest anything other than air has got into the system due to the run off through the CH system.

With the hot water on and heating off Hot water is being returned to the boiler and it shuts off after a few minutes, presumably as it thinks the water temperature has reached it's optimum.

All that said hot water is reaching the coil but is not departing from it clearly it is then blocked with air or otherwise.

Given the fact there is no way to get at it is there a workaround to clear the blockage or am I looking at a new copper cylinder?

Thanks for your all your help btw.
If the pump is running on HW only then the water from the boiler should only be going up to the cylinder. (Even with heating on I would assume this is the path of least resistance). If the water cant get through the coil, (if it was an air lock i'd think the pump would push it through anyway), it can only go up the vent into the tank, then return via cold feed to cylinder bottom connection, thus bypassing the coil. (Usually though the water is being pumped into the cistern faster than it can return and the cistern overflows.....)

Ive never come across a blocked vent, but thats not to say it couldnt happen, which would cause an airlock as the trapped air cannot escape. Its also a vital safety feature of the system so needs to be clear. You could try connecting a hose to the vent, and using mains pressure backfill the system, the water should return via the cold feed into the cistern. Keep a close eye on the level though! This would ascertain the vent is clear.

Cylinder connections could be cut, coil flushed and cleaned and cylinder reconnected. That would rule out any blockage there, and saves expense of a new cylinder if the coil is not the issue. It does seem strange it worked ok prior to your emergency drain down, but providing the vent is clear I cannot see it being an air lock.
Hi there Geezer
I've come across a similar problem - did you figure out what this was in the end?
Thanks for any help you can let me have


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