Air Lock in Mixer Shower

[diynoob]

I had to drain down the hot water to fix a leaking isolation valve. It's an open vented system with an oil boiler.

All outlets were spluttering afetrwards. The mixer taps were easily fixed by covering and forcing the cold water up the hot. There is a downstairs bath with a mixer that was difficult. Tried it a dozen times and finally after covering for 3 minutes forcing the cold water up the hot it seems to be OK now.

But upstairs theres a thermostatic mixer shower (with a separate pump) that is still air locked. The pressure goes up and down when in use. I tried turning off the pump and then removed the shower head and covered the end and turned on to try to get the cold to flow up the hot pipe. I did this for 12 minutes and it makes no difference. I think the shower must be preventing the cold flowing up the hot.

Any advice?

 

[terryplumb]

thermostatic mixer valves usually have non return valves fitted ,inside where the water enters the valve. so they dont àllow backflow. the hot and cold are usually at the same pressure ,and both from the loft tank. did you drain the loft tank when working on the hot water leak ? if you did ,cold to shower may be airlocked too. is the mixer a horizontal bar type by any chance ?? do you have isolation valves on hot and cold supplies to the pump ?

 

[diynoob]

Yes it's a horizontal bar. There are no visible isolation valves on the shower. Could be some behind the tiles I guess.

 

[terryplumb]

look at pipework going to pump.see if you can isolate BEFORE the pump. hot and cold supply's.if you can you will be able to remove the mixer and we can give you more info.

 

[diynoob]

Looks like I could isolate at the pump.

 

[terryplumb]

looks like the isolators are integral in the hoses ,can't see any others ,oh well. try isolating hot and cold. and electrically isolate the pump. then remove the bar mixer valve.( whilst off check / clean filters and ensure non return valves are moving freely ) then open the cold isolation valve and let water run out the open pipe in the shower ,hopefully it will splutter then run constant .close isolation valve. then repeat the exercise on the hot. by removing the valve and having open pipework without resistance can very often get air out the pipework. try it and report back.

 

[diynoob]

Thanks for your help. The hot spluttered but does seem to be flowing nicely now. I'll reassemble and let you know.

 

[terryplumb]

good stuff ,what about the cold ?

 

[diynoob]

The cold is fine. I've not had any issues with cold at any outlet. The hot is still not right though. With the shower on cold it works normally but on hot it's still spluttering. The hot on the bath is doing it too.

Since its just the upstairs shower and downstairs bath that have the problem it's possibly the same air lock affecting both. The bath is easier to tackle since its a mixer. I've blocked it and forced the cold up the hot for 4 minutes now and its still spluttering. Shall I try doing it for longer?

 

[terryplumb]

have you checked the water level in the cold water storage cistern ,in loft I assume ? can you confirm if any cold taps ( not counting the kitchen sink ) are fed directly from the mains and if so which ones. if you are getting hot water coming out of your taps ,although they splutter ,if you leave them running do they eventually go dry ?

 

[diynoob]

It's an odd house but yes the tank is sort of in the loft. It's not possible to see into it, but if I poke a stick into it it does seem low, only about a third full. Not sure I can bend the float valve though (assuming there is one). The tank is only a few inches from the roof and a few inches from the wall at the side where the water enters.

If I run the bath, the hot tap splutters but it does not run dry. Thanks again for your help.

 

[terryplumb]

when you worked on the hot water to sort your leak ,did you close down those red wheeled headed valves on the loft tank ?

 

[diynoob]

Yes that's right. I couldn't reach to tie up the float valve, so I closed those gate valves in the picture. When fixing the leak, I didn't have to drain out all the water. Hardly any water came out because I'd created an air lock. Wasn't expecting it to cause this much grief though!

 

[terryplumb]

ha ha ,welcome to the world of plumbing ! anyway those valves are called gate valves ,and they are notorious for not closing fully and more importantly not opening fully after they have been closed. on what you have told me so far I think you are "sucking air " into your hot water pipework. I suspect that one of those valves ,which is on the pipe that feeds cold water to the bottom of your hot water cylinder , is not fully open and the flow is significantly reduced. so when you open hot tap the water level in the vent pipe drops and air is getting sucked in. the level of water in the cold water storage cistern in the loft is too low and you will need to address that problem as well. I suspect that when you were working on your hot water leak ,that you also closed off your main stopcock on the cold mains feeding the loft tank ,and maybe opened cold taps as well as hot to drain water out before you sorted your leak . am I correct ??????

 

[diynoob]

Mate I think you've cracked it. When I reopened the gate valves I was scared to damage them so didn't force them. I've checked again and the one that connects to the base of the HW Cylinder is indeed not fully open. Opened it now and will do some more testing. Will remember to count the turns next time I mess with gate valves...