Boiler inflow to indirect HW cyl

[oldschoolmechanic]

My HW tank has developed a small leak where the inflow from the boiler attaches.

I have a feeling that replacing the HW tank is ultimately probable but would like to try a repair first (even if it only lasts a few months - money is tight etc).

I know I need to relieve the water pressure before attempting a repair but I'm not familiar with how the coil is joined to the cylinder so my question is:

Is the leak likely to be from the stored hot water in the cylinder (is that even possible on that joint?) or the boiler circuit?

Reason for asking - I'd prefer to only drain one if I can. Thank you.

 

[MeldrewsMate]

From my experience leaks of this kind originate when the cylinder is installed and 1" female to 22mm compression adapters are used and overtightened, resulting in the coil twisting with respect to the cylinder wall.
The coil is secured, in a standard copper cylinder, with a 1" nut on the male end sandwiching the cylinder wall between it and a swaged part of the coil, usually with a fibrous washer to seal. Once twisted the seal starts to break down and eventually a leak issues from it.

You may be able to re-tighten the 1" nut after draining the cylinder AND the heating circuits and removing the heating pipework and the 1" female adapter, though there is a high risk of twisting the coil further and exacerbating the leak, so best advice is to check stocks at your local supplier first, and be ready to change the whole cylinder (immersion heater spanner present?)

Of course, just because I've seen it many times it doesn't necessarily follow that yours is the same.

MM