Gravity cold constantly airlock

[Best]

I have came across a strange one I can't solve.
Have been to a job probably 5 times over many months. This plumbing is original several decades old, without precious bother. The elderly couples toilet and cold bath tap stop flowing from gravity tank fed. First time I went I just quickly cleared the air lock by linking the bath hot and cold taps together with a hose for several seconds. But same thing happened again after a few months, so I checked CWT in loft and replaced the ballvalve. Everything seems fine, - ballvalve flows well, cold pipe leaves the CWT only a foot and drops down airing cupboard and then below bath. No power shower or pump exists, so no issues with tank being drained at any time.
How can a cold pipe airlock? They rarely use the cold bath tap, (as have an electric shower) so only the cold flows to the toilet regularly.

 

[ShaunCorbs]

Bath cold tap ducking air in ?

 

[Best]

Bath cold tap ducking air in ?

Would that be possible? Bath taps are 2 Peglers old style Sequel taps that have real packing nut type works. I replaced the tap washer on the hot tap because the customer mentioned it was hard to turn off, - turned out old washer was rock hard. I didn't replace the cold taps washer.

 

[Shower Engineer]

The foot before it drops down does it rise or fall from the cistern?

 

[ShaunCorbs]

Would that be possible? Bath taps are 2 Peglers old style Sequel taps that have real packing nut type works. I replaced the tap washer on the hot tap because the customer mentioned it was hard to turn off, - turned out old washer was rock hard. I didn't replace the cold taps washer.

worth a try

 

[Best]

The foot before it drops down does it rise or fall from the cistern?

It is falling from the cistern. The ballvalve is on opposite side of tank to the outlets. It is a 50/70 gallon round cwt. All work is original 50 plus years, except cwt which was replaced probably 40 years ago and the bathroom is 15 or so years old. All work is in copper.

 

[Best]

worth a try

Yes, I think you are right Shaun. Kicking myself I didn't replace the cold tap washer yesterday. I had actually just turned both stopcocks off from cwt (as weren't labelled). Getting the seized works screwed off the hot tap was hard to do without risking damaging the tap. Thankfully I have a new Knipex parallel jaw wrench which is perfect for gripping chrome tight without damage.
I will go back and replace the cold washer to rule it out.
Thank you to both of you for your thoughts!

 

[ShaunCorbs]

Yes, I think you are right Shaun. Kicking myself I didn't replace the cold tap washer yesterday. I had actually just turned both stopcocks off from cwt (as weren't labelled). Getting the seized works screwed off the hot tap was hard to do without risking damaging the tap. Thankfully I have a new Knipex parallel jaw wrench which is perfect for gripping chrome tight without damage.
I will go back and replace the cold washer to rule it out.
Thank you to both of you for your thoughts!

there always the best esp trying to get the top off without damaging it love the screw type hate the push type

and they are a good grips esp for brass fittings that are too big for spanners

 

[mfgs]

Is it definitely air? I have had a gate valve which was intermittently failing and dropping closed shutting off the water supply.

 

[Best]

Is it definitely air? I have had a gate valve which was intermittently failing and dropping closed shutting off the water supply.

Yes, bath cold is the first supply and water just trickles if turned on. Toilet cistern is next and final supply and doesn't really fill. When I push the hot up the cold tap I can hear air going into cold tank. No gatevalves - just stopcocks.