Leak and losing pressure in Gas CH system

Calibos

Early last year we had a leak in the Gas CH Loop pipe going into the Emmersion Cylinder. Stained celing below etc. A plumber aquaintance fixed it for free by tightening the flange or nut or whatever its called where the Heating Loop pipe enters the Cylinder. However later that year we realised the CH system was losing pressure from its normal 1.5bar ddown to zero when the boiler stopped working. Topped up the system back to 1.5bar but it kept losing pressure over the course of a few days. Should have got it sorted straight away but this or that came up and I'd end up just topping the system back up. Sometimes it would be days but other times it might be a few weeks for the presssure to drop.

Figured the Emmerion leak was too much of a coincidence but couldn't rule out a leak in the downstairs heating zone under the concrete floors (not upstairs heating zone because a leak of that amount would have shown in the ceilings downstairs by now like the original Emmersion leak) Posted here late last year IIRC asking about inhibitor and flushing the system because I know enough to know that I've probably completely replaced the full volume of water in the system at this stage from refills and left it so long now without inhibitor and oxygen rich water that the system is probably starting to fill up with gunk. That said this Winter all Radiators on all 3 stories are still piping hot from top to bottom.

Still didn't do anything about it as Winter ended and Heating zones stopped getting used because I had a million other things to think and worry about with the death of my Mother. Now that my head is in the right place again and I realise I have to get back on top of the house maintenance again, I want to get this sorted now. Am I right in thinking that the fact that the system is still losing pressure this Summer just as fast and still needing to be refilled despite neither Heating zones being used at all with theoir zone valves closed and only the Hot Water Zone in use, that this does indeed point to the Emmersion heating loop pipe being the culprit. ie. The tighteing of that nut and the stopping of the leak on the outside kind of just pushed the leak inside the cylinder. No physical evidence of the leak because its now actually leaking Hot-Water Zone Boiler water into the cylinder and thus the House Tap/pump shower Hot Water?

Does 2 years without inhibitor mean a full flush is needed?

Can I fix the leak DIY with leak sealer powered into our towel radiator in the bathroom (Has convenient top up and drain nuts unlike conventional wall rads). ie. If I turn all zones on and all zone valves are open, will the sealer get from the towel rad and upstairs heating loop back to the Hot water loop in the emmersion?

Will the sealer even work correctly when its not plugging a leak to air but rather a submerged leak inside the cylinder so to speak. Does the sealer need to react with air at the site of a leak to fill and bond to the hole etc. (Might explain the time variability of pressure loss. ie. certain amount of pressure inside the cylinder under water slows leak and running hot water taps and showers relieve pressure and leaking speeds up. So depending on shower and tap use varies the amount of time it takes for the pressure to drop down to the .25bar I usually notice and top it back up from)

Or am I looking at a large Plumbers bill before Winter arrives to replace the Emmersion/Hot Water Cylinder and Hot water loop pipe and flush the entire system and then fill it all back up with inhibiter included?

TIA

10-10-20

Hi! That post is way too long, but I get the gyst of it!! My sympathies on your mother's passing.

Leak sealers work by reacting to oxygen, so if the leak really is in the immersion cylinder, then it won't work.

You've got to figure out where the leak is. I'm not sure if an external cylinder flange leak would become internal to the cylinder like how you describe, but anything's possible I suppose. The one thing that I noted is how you haven't mentioned hearing any air within the system, normally that's a good indication of a leak into open air and you obviously wouldn't get that with a cylinder leak.

Normally if the cylinder coil is leaking you get symptoms such as the hot water coming out of the expansion pipe in the attic. Example of the symptoms documented here in this old thread:

https://www.boards.ie/discussion/2055815601/heating-coil-leaking-in-hot-water-cylinder

In terms of inhibitor, yes it's likely that all of the inhibitor has washed out of the system, replacing it would be important, but I personally don't see a need for a full flush as you aren't getting air into the system (and hence no excess oxygen bubbles) and likely little sludge.

Adding inhibitor into a rad will be fine, it will mix with the rest of the system as long as you open the valves and run the heating for a short period.

Anyway, most critical objective is to try identify whether you have a coil leak or not.