Air lock

[Gedling]

After 5 happy years using my Mira gravity fed shower I get air locks in the hot feed pipe. I clear the problem by diverting mains pressure water through the wash basin mixer tap but it all commes back again within a couple of uses. Where could it be coming from - I've got no apparent leaks and in any case the whole system is under pressure. The system has a vent on it. The piperun is long but it worked for 5 years - anyone got any ideas

 

[Bahco]

Check your ball valve operation. Run your shower and watch to see if your tank is refilled properly and does not run dry

 

[Gedling]

Thanks for the suggestion but it wasn't the tank running dry. I connected the rising main to the highest point on the shower hot feed (with double check valve and isolating valve) and flushed it through. This drove out the air trapped in the pipe. The lesson here is that air locks can be very difficult to shift especially if the pipe run is long.

 

[ChrisR]

Seems to leave the question of how the air got in there? Odds-on Bahco is right.

 

[Gedling]

The tank water level did not fall much when everything in the bathroom was running - and that was after I cleared the blockage. I think that air entrained in the can be released slowly especially when temperature changes occur as would happen in such a pipe. The air would build up until it causes blockages. The fact that the pipe is long with many bends and changes in level probably doesn't help.

 

[ChrisR]

Er, still seems to leave the question of how the air got in there?
Air tends to dissolve into water, not form bubbles, unless in (& therefore after) a pump.