I had a leaky hot water tap on a shower, so I replaced the plastic
rubber O ring bit inside and this stopped the leak.

But two weeks later (and possibly unrelated) the same tap when you
turn it on puts out no water, it takes about 1 minute for water to
start coming out.

I am guessing I have a leak in this line. But the pipe goes directly
through a solid double concrete wall to the hot water system so there
is no access what-so-ever. Because its on the hot water line I can't
see my meter moving and I haven't noticed my hot water service filling
unusually.

Does anyone have any ideas on how to figure out what is going on?

Does anyone have any ideas on how to figure out what is going on?

Could the o-ring be sticking ?

wrote

I had a leaky hot water tap on a shower, so I replaced the plastic
rubber O ring bit inside and this stopped the leak.

But two weeks later (and possibly unrelated) the same tap when you
turn it on puts out no water, it takes about 1 minute for water to
start coming out.

I am guessing I have a leak in this line. But the pipe goes directly
through a solid double concrete wall to the hot water system so there
is no access what-so-ever. Because its on the hot water line I can't
see my meter moving and I haven't noticed my hot water service filling
unusually.

Does anyone have any ideas on how to figure out what is going on?

If the seal isn't quite right it could be stopping water coming out but not
stopping air getting in.
Is it possible that the water is draining back towards the source? If so,
the delay would be waiting for water to refill the pipe to the tap.

Phil