This is something I've never seen anywhere. The blockage only effects the hot supply to the bath/shower thermostatic mixer valve and i first noticed it about 6-7 weeks ago when the flow from the tap gradually slowed to a trickle over a few days until it became useless. I removed the valve to find a yellow fatty substance blocking the filter in the hot inlet to the valve. I thought it a bit strange at the time but just removed it and re-fitted, and all worked well. Thing is it happened again tonight as i noticed the bath filling up slowly when running it for the kids. Removed the valve and here's what i found. The first pic shows the material as i found it on the filter and the second one after removal. On closer inspection it felt a bit gritty so i dried it out and it appears to be like a very fine sand, as shown in the later pics. It is only this tap/valve that has been affected by this blockage and as i have taken a supply (several years ago without any problems until now) from below the bath to feed an outside tap at the rear of the house i can only assume that the check valves have become knackered for some reason and no longer work as they should. In twenty-odd years I've never come across this problem before. Have any of you lot, by any chance?
Never had that kind of sediment , found plenty of boss white where previous plumbers have been a bit generous on fittings which has worked it's way through the water supply. Is the hot water fed from a cylinder? That'd be the first place I'd investigate
No, its a combi boiler. As i said, I've never seen it before either. The first time it was a bit of a "WT' moment, until it happened again several weeks later.
You can take the man out of the theatre, but you can't take the theatre out of the man. Great days, eh?
The first photo definitely looks like some kind of algae which can form even in anaerobic conditions. Wonder if that is what it is, Would probably be binding itself to any sediment in the pipework which is why you get the gritty stuff on drying out.
Could be a few reasons but maybe consider temporarily using the bath mixer without the filter just to flush out any debris hanging around. which gas combination boiler do you have ?
Its certainly got me stumped. It has got a kind of fatty appearance when wet but after drying it looks exactly like very fine grains of building sand.
The feed to the outside tap is tee'd off from below the hot supply to the mixer which is why i initially suspected a fault in the check valves. How any back flow could occur, i don't know as it's never been drained down from there. Its a potterton promax he. A very good boiler from my experience.
Not sure what that could be. I wonder is there sediment on the walls of the inside of pipes? Another thought, - does the bath mixer have flexi hoses connected to it? Although I would think bacteria growth would not be gritty
Its weird alright. If it had only occurred once i would have forgotten about it by now, but twice in as many months has certainly got me thinking. Its blocking the inlet to the valve so its definitely coming from the supply side. I did wonder about the possibility of grit/dirt entering the mains supply to the house because of external work carried out by the utility provider as CGN has suggested, although i would have thought that such a scenario would also effect the cold supply as well. As its only the hot, i can only think that the outside tap is somehow trickling in this sediment, or, that maybe the heat exchanger in the boiler could be causing it by slowly releasing particles of scale on the heat exchanger into the system.