Sounds as though the leak has gotten much worse Mike.
The boiler has obviously shut itself down cause of lack of water in the heating system.
Before we started 24/7 htg on Sunday morning, the mains ingress flow was about the same as when we discovered it. As the exp. tank was operating as normal (ballcock, that is), the pipework couldn't have run out or got short. Since Sunday this has been check 3x per day to make sure that the exp. tank level remained constant with no refill with 24/7 htg.
At least you have immersion heater backup for water. Hope you have some electric heaters too. If not, might be sensible to get some in.
Yes, thanks; because of our old boiler failure last January (now there's a coincidence !!!) I've bought a couple of heaters and already had a large radiant and another convector. Have had an oil-filled rad in the bathroom since the new installation (needed as no residual red. heat under new pumped system)
I've asked my plumber if I can turn on the immersion, just to be safe. Can't see why not but this new pumped system is Heathen Greek to me.
I think the problem is in the hot water cylinder.
You and me both, though not the actual cylinder but the pumped piping operating it. However, this is separate from the leak but sth here was just too noisy to be right. This as a cause of the error code shutdown as the boiler has coped with the leak for well over a month by my reckoning.
Could you disconnect the flow and return pipes for the suspect underfloor loop at the underfloor heating manifold and blank them off or install a short "dummy loop"? If this "fixes" the leak and the problem, then at least you know for sure where the problem is (assuming you still have doubts).
Well beyond my capabilities and expertise, I'm afraid; We're now 99.5% sure there's a leak in the sub concrete floor pipes since I drained down (though the leak) last night; we could hear it clearly (hence no sleep).
Thank you again, gentlemen. My plumber is without phone at the mo' and isn't the best email communicator but I'm now waiting for him to either contact me or call round; he has all the details of what's happened. It's a waiting game but he has mentioned lek sealant and/or connecting all the rad's overground. I'm no plumber but can't see how that's going to work with a number of doorways + French window.