Hope you guy's can help/advise 
Just over a week ago, I removed the kitchen rad in order to plaster the wall behind it, at the same time, removing the bathroom rad so the wall could be tiled. I replaced them both yesterday, adding inhibitor and topping up the system, released the air in all rads and run the heating to make sure everything ran o.k. ( no leaks ect. ) pressure at 1.5 everything seemed to be fine. The wife started to run the bath last night, but said that the hot water had started to run only warm. I turned the tap off, turned it back on, it instantly ran hot, and sure enough it soon only ran warm, I did this a few times, sometimes it even ran cold. I told the wife to turn the hot tap on whilst I went and viewed the boiler, tap on, boiler fired up o.k., instant hot water, but soon ran cold/warm again although when the hot tap ran only warm/cold, the boiler still ran as normal, turned the tap off, the boiler shut down as it should. Now then, whilst we were carrying out this little test, I noticed and felt the house getting warmer sure enough, ALL the the rads were HOT, the heating had not previously been on, only earlier in the day when I checked the system after re-connecting the 2 rads, I can't understand it at all So !!!!, I left it untill this morning untill everything had cooled down, got up (YAWN) turned the hot tap on in the bathroom, instantly hot, then warm, and sure enough, ALL the rads started to get hot whilst ever the hot tap was running, CH is switched off, but still they get hot, *%$£@"# Pressure is still o.k. but now I'm confused. The wife wants to instantly call out an engineer/plumber (mega bucks), but I thought I'd consult you guy's first. We live in a flat, so completely draining/refilling the system and starting again would be difficult. The boiler and system is 2 years old ( Vaillant Turbomax Pro 28e )
Just over a week ago, I removed the kitchen rad in order to plaster the wall behind it, at the same time, removing the bathroom rad so the wall could be tiled. I replaced them both yesterday, adding inhibitor and topping up the system, released the air in all rads and run the heating to make sure everything ran o.k. ( no leaks ect. ) pressure at 1.5 everything seemed to be fine. The wife started to run the bath last night, but said that the hot water had started to run only warm. I turned the tap off, turned it back on, it instantly ran hot, and sure enough it soon only ran warm, I did this a few times, sometimes it even ran cold. I told the wife to turn the hot tap on whilst I went and viewed the boiler, tap on, boiler fired up o.k., instant hot water, but soon ran cold/warm again although when the hot tap ran only warm/cold, the boiler still ran as normal, turned the tap off, the boiler shut down as it should. Now then, whilst we were carrying out this little test, I noticed and felt the house getting warmer sure enough, ALL the the rads were HOT, the heating had not previously been on, only earlier in the day when I checked the system after re-connecting the 2 rads, I can't understand it at all So !!!!, I left it untill this morning untill everything had cooled down, got up (YAWN) turned the hot tap on in the bathroom, instantly hot, then warm, and sure enough, ALL the rads started to get hot whilst ever the hot tap was running, CH is switched off, but still they get hot, *%$£@"# Pressure is still o.k. but now I'm confused. The wife wants to instantly call out an engineer/plumber (mega bucks), but I thought I'd consult you guy's first. We live in a flat, so completely draining/refilling the system and starting again would be difficult. The boiler and system is 2 years old ( Vaillant Turbomax Pro 28e )