Air getting into hot water pipes

[goateater]

Hi guys, I can get the air out by connecting washing hose pipe to hot pipe and run cold water though the hot pipe

But its happening every 3-4 weeks (been like it for 20 yrs or more) so want to try to stop it

Live it a dormer bunglow, Cold water tank in roof, hot water cylinder on first floor (dormer level)

so cold water tank is about 3 ft higher than top of vented hot water cylinder, hot water cylinder is about 4ft tall

feed from cold water tank is 28mm (though that is might give more push when hot taps turn on,)

hot water cylinder outlet is 22mm, goes to a Tee connector one side has vent pipe other drops to first floor level to feed downstairs Bathroom/shower & kitchen, downstairs Utility room, up stairs sink and power shower pump

I’ve got no leaks so can’t see where the air gets in to the hot pipes

Any suggestions ?

One suggestion I had years ago was insulation foam from the had got inside the hot water cylinder before it was installed and is partly blocking the outlet pipe allowing air in (though the vent pipe) when the hot taps are on

 

[terryplumb]

Is the hot water being drawn off quicker than the loft tank is being replenished ?
Run a hot bath tap plus one other hot tap ,and watch the loft tank. Is there a second outlet from loft tank feeding any cold taps / toilets etc , or is every cold outlet mains fed ?
Is the shower pump remote or built into the shower ?
If there are several hot water outlets in use at the same time ,particularly using a pump, the loft tank may be getting drained faster than its replenishing

 

[Johntheo5]

"hot water cylinder outlet is 22mm, goes to a Tee connector one side has vent pipe other drops to first floor level to feed downstairs Bathroom/shower & kitchen, downstairs Utility room, up stairs sink and power shower pump"

The vent should, where possible rise straight up from the cylinder top, if the HW outlet & vent is taken from the side of the tank then its inevitable that air will eventually build up in the cylinder top and force down the water level to allow air ingress to the HW outlet.

Can you post a photo of the HW cylinder showing the vent and where the HW is drawn off?.

One of these might help.

 

[goateater]

Vent and hot water draw off is taken from top of tap (sorry if I didn't make that clear)

 

[Johntheo5]

Except you have a problem like suggested in post #2 then installation should be like below.
The "warix" flange is like the one I showed above, under various names like surrey flange.

 

[HERTS P&D]

Check the float valve in the loft is filling/working correctly when the bath taps are open?

Andy

 

[goateater]

sorry about the delay in getting back
no photos of setup yet
hot water pipe comes out top of the tank *right angle then on to Tee connector" other ends of Tee 1 is the vent pipe up to the cold water tank, the other drops tp floor level feed to all hot water outlets
there is no separate pipe feeding the standalone twin shower pump, the hot & cold water tap off the house hot & cold water pipes
only Kitchen cold tap comes off mains, all others fed from cold water tank
cold water tank has one outlet pipe that feeds hot water tank and all cold water outlets
cold water tank fills up correctly and there is good head of water in the cold water tank when showers or taps are running
it is an old system been in here for 40 yrs, I've lived here about 30 yrs