Airlock or blockage in HW flow

[mr chumleywarner]

Familiar story I'm afraid. I drained the water down to replace a tap and after refilling the hot water is now not flowing. The water spurts and then flows to a trickle then stops. Upstairs there is no hot water flowing at all. Trying again an hour later gives another burst of activity then nothing.

I've tried the suggested way to fix it by blocking the kitchen mixer tap with both taps open to force the water up the hot pipe. This results in a short flow of water which eventually fades to a dribble.

I did think there was a blockage from the cold feed to the cylinder but when I got up in the morning the bottom of the feed pipe near the cylinder was hot. Running the hot tap in the kitchen then cooled the pipe down suggesting some flow. The flow out of the cylinder is also hot up until it disappears under the floor boards. I'm guessing if there is a blockage its under the floor before the split between the upstairs and downstairs taps?

When I try to drain the system by turning off the mains and opening the cold and hot taps in the downstairs toilet nothing other than a few spurts come out.

Is there a way of finding out if there is any water in the cylinder (other than by clanging it which doesn't tell me much). One thought was I could see how full it was by doing the tap connecting trick and seeing how long it takes to go out of the vent but will this do more harm than good?

Are there any other things I can try to pinpoint the cause?

Thanks in advance

 

[HERTS P&D]

'I've tried the suggested way to fix it by blocking the kitchen mixer tap with both taps open to force the water up the hot pipe. This results in a short flow of water which eventually fades to a dribble.'

Do the above again for at least 30 seconds then while you are doing it get some to open the basin tap to check water flow then close and try the bath tap.

Or use a wet and dry vacuum to suck out the air from the hot bath tap.

Andy

 

[mr chumleywarner]

Do the above again for at least 30 seconds then while you are doing it get some to open the basin tap to check water flow then close and try the bath tap.

I did this this morning but maybe for about 20 seconds with both taps open - some water spluttered out of the bath tap in the upstairs toilet but none from the upstairs basin. I could maybe try it for longer tonight with one tap open.

Or use a wet and dry vacuum to suck out the air from the hot bath tap.

Interesting! I only have a Dyson though which I don't think will handle water - although I could risk it if I pull it off the tap quick enough...?

 

[mr chumleywarner]

Fixed.
Luckily I got hold of a plumber who after failing to get the mixer tap trick to work had the same idea with the wet/dry vacuum. Clearly a trick of the trade.

Thanks to Andy for replying.