Radiators heat fine. But taps are luke warm at best and seem to to loose heat very quick. Glowworm boiler. Do the glow worms heat rads and taps are 2 different temperature settings.
I did chang lagging jacket as old one smelled. And was even burnt onto tank in parts. New one is still on quite snug. With a maye 2-3cm gap exposed here and there. I cant imagine nits enough for heat to escape as quickly. Before water in tank would still be warm enough 8-9 hours later. Now have to use lukewarm water pretty much with in the hour.
Is the hot-water zoned or does it normally heat the rads and water at the same time? You might have a stuck valve preventing the hot-water cylinder from being isolated when the rads are on. That can pull the heat from the cylinder depending on how the boiler is working.
But the lagging jacket should be fitted tightly and without gaps too, so that could be adding to the issues.
Heating is zoned. Issue is there even on days where heating is not on? I will check if heat flowing through both motorized valves. Would that indicate what you are saying ?
Any progress Allycavs ? I have the same problem. Separate circuits. Rads hopping after 1 hour.
Hot water is on separate switch, barely hot after 1hour.