I'm in the UK with a small modern, well insulated, double glazed home heated by a traditional gas boiler.
My heating had been achieving room stat temperature within 30 minutes but is now taking at least 3hours. After the boiler has run continually for about 2hours I think it probably cuts out on the boiler stat (ie it is not up to temperature on the room stat - also confirmed with seperate thermometer). It switches off for a few minutes and then comes back on again and continually cycles the boiler on and off for at least another hour before the room stat temperature is reached. I have monitored the rise in temperature closely this morning and find that the inside temperature does not even keep up with the rise in the external temperature!
If I only run the "hot water" part of the system (ie no central heating) the hot water gets to temp within about 45minutes. The problem appears to only be with the central heating side of the system.
New room & boiler stat have been fitted. The pump "sounds" to be running fine and all radiators are uniformly hot across their entire surface.
Does anyone have any suggestions as to what the problem might be please?