4 Mar 2017
Reaction score
United Kingdom
Have a header tank and hot water tank. Turned off cold mains in and drained both as wanted to fit isolation values in downstairs toilet. There was no apparent isolation value on the hot tank out.

Did job and turned mains cold back on header tank fills but hot water tanks doesn't (provides a dribble out well very weak flow from hot tap in kitchen dribble in bathroom on first floor and nothing on top floor). The top floor cold water doesn't work either which I think is fed from header tank.

Cold mains taps in kitchen and ground floor loo work fine. Bathroom cold slow but always has been but perhaps not as slow as it is now.

I am thinking air lock or blockage as result of draining. If former how to resolve if later any easy answer beyond call a plumber?!

The plumbing was installed before we arrived so bit blind on exact piping and make up.
Sponsored Links
If the large tank in the loft is full, then you have an airlock.
You can overcome this by feeding cold water under pressure up the faulty tap, which forces the air back up into the tank.
John :)
Which means that you need a hose attached on to the cold and hot taps, and that will force water back up the hot tap, into the tank. Do you have a garden hose, and tap fittings.
Sponsored Links
If you got a mixer tap in the kitchen try putting your hand over the outlet and turn both taps on, it will push the airlock back to the loft unless you got nrv fitted.
Presumably any hot tap that isn't working would do to push air back with the hose. There are 6 around the house all bar one is a mixer tap.

I turned the boiler off completely. Can the heating be turned on and not the hot water or is it better to leave both off until solved.

And if puffing on a tap to get air out doesn't work I guess the answer is find a plumber?
I should add that when I turn a hot tap on and I get some flow which then fades to a very weak flow and then if I turn the tap off and leave for an hour or more and the same thing happens would suggest a partial blockage. If there was an air lock would I get any flow at all other than air hissing and gurgling in the pipes or can an air lock be silent and also allow a partial flow.
If you got a mixer tap in the kitchen try putting your hand over the outlet and turn both taps on
A kitchen tap is required have separate channels for hot water and cold water to prevent drinking water drawn from the tap being contaminated with the hot water. These two channels should extend separately to the end of the spout. You hand will have to allow water from the cold water channel to get back into the hot water channel.

The method often works but if it is a legal kitchen mixer tap then blocking the spout with a flat hand will not work. Instead try pulling a rubber glove over the spout which will allow cold water to get into the hot water channel.
Have you actually looked in the Cold cistern in the loft? You'd be amazed what has been found in those in the past, blocking up the outlets.....

I would also expect cistern fed cold supplies to be on independent pipework to the hot supply, how many pipes are there coming off the Cold water cistern? For one to airlock is one thing, for both maybe too much of a coincidence.

You're unlikely to have a isolation valve on the hot water out, with a normal cistern and cylinder arrangement, any valve should usually be fitted between the cistern and cylinder, (yesterday was probably the ideal time to fit one if there isn't anything there!)

DIYnot Local

Staff member

If you need to find a tradesperson to get your job done, please try our local search below, or if you are doing it yourself you can find suppliers local to you.

Select the supplier or trade you require, enter your location to begin your search.

Are you a trade or supplier? You can create your listing free at DIYnot Local

Sponsored Links