Symptom is hot water to bath starts off fine and then slows down - takes a long time to fill the bath. It's a mains pressure system.
I've just had the boiler serviced, which has fixed the central heating not working on the top floor (found a brilliant Valliant technician). He said the hot water is almost certainly a valve 'collapse' problem and will be giving me a quote to cut it out and put in a new one. But can't the valve just be repaired, and how to actually pin down the fault?
E.
the answer to "can't the valve be repaired?" reminds me of a colleague whose Mini developed a gearbox fault. "Recon box" said the dealer, bu cooegue said "it's only 2 year old - mend it". So, they did and it cost more than fitting a recon box wuld have done.
In article , eastender writes
It could be the tap. Does the sink suffer the same problem? Dismantling the tap may be a simpler solution (if the cause) and likely DIYable.
When you say it's a mains pressure system, do you mean that you have a system which stores hot water in a mains-pressure cylinder, or a combi boiler which heats mains pressure water as it passes through?
Do you have other taps (wash-basins, sinks, etc.) served by the same system? Do they all exhibit the same symptom, or is only the bath tap affected?
In message , eastender writes
What valve?
It's a system which stores hot water in a mains-pressure cylinder.
All taps affected and are served by same system, bath particularly so though.
E.
Good question. I'm not sure what he was talking about...
E.
If you are storing hot water at mains pressure, there's going to have to be a valve to stop hot water getting into the main if the pressure drops (like a burst pipe under the road.
Sounds as if the valve, is a pressure reducing valve which has collapsed.
I have just had my (different) boiler fixed due to a low DHW Flow. The fault was a collapsed O Ring next to the flow restrictor.
A previous boiler used to have a spring loaded reducer. I think that the normal flow was unrestricted - but as the tap was opened further there would be a "clunk" from the boiler as a valve closed in response to the flow and diverted the water through a restrictor orifice.
OK, I think I know what the problem is. Since all taps are experiencing it, it's a problem with the whole system and not just with one tap.
Since it starts off fine, it indicates that there's no problem with the pipework between the cylinder and the taps. Since it's a mains pressure cylinder, you'll have an expansion vessel somewhere - either an external pressure vessel or an internal bubble. When the cylinder heats up, the water expands, and a non-return valve stops it going back into the mains, so that it has to compress the air in the expansion vessel.
When you first open a tap, the initial flow is provided by the stored energy in the expansion vessel without needing any new mains water to come in. Once the pressure has reduced, new mains water is required for expelling the hot water out to the tap. If the flow of this mains water is restricted, the flow to the tap will be slow.
I mentioned a non-return valve just now. This will be on the mains input side to the cylinder, and may be combined with a pressure reducing valve
- to prevent the pressure in the cylinder becoming too high if the mains pressure is more than about 3 bar. Or there may be two separate valves in series. Either way, that's where the problem lies. Something has gone wrong with one or other of these valves (or with the combined valve if that is what you've got) which is restricting the cold water flow more than it should.
I had similar symptoms on a megaflo unvented HW system. That turned out to be a faulty pressure reducing valve on the cold-water inlet to the HW cylinder. I got the PRV replaced, which cured the problem.
My PRV was connected to the copper pipes with compression fittings, so it was a fairly easy replacement, with no need to cut anything out.
That sounds like a good diagnosis to me.
I've had tap washers distort when they get hot (i.e. when tap has been running for a bit). Try changing the tap washer.
Yup that sounds like an eminently plausible explanation to me. See part
3 on the diagram:Another (similar) possibility is some systems are built with a thermostatic blending valve on the outlet of the cylinder to limit the maximum temperature delivered to the taps. This is another single point of failure that could limit flow - although in this case it would be when that valve gets hot rather than when the pressure stored in the expansion vessel is released.
Yes, that's an excellent explanation, many thanks. I've had a good look at the pipework and there are two Honeywell valves in series that look likely candidates. I don't think this is a DIY job (for me) so will chase up the boiler guy and see if he wants to fix it.
E.
Would it really be the end of the world for a bit of hot water to go back into the mains?
Might depend on your attitude towards prison, I suppose.
Seriously though, it *is* illegal because your HW system could be harbouring all sorts of bugs (legionella, etc.) which could be fed back into other people's clean water supply. Might not be very likely, but the possibility is there.
I've used the hot tap to fill a mug for hot chocolate loads of times. It's much quicker than waiting on the kettle.
No it isn't. Just think how much water would have to be fed back before it left your premises and got to the nearest junction point. Just how much expanding does your tank do?!
It would, probably, contaminate your drinking water. So, for someone, it could be the "end of the world".
HomeOwnersHub website is not affiliated with any of the manufacturers or service providers discussed here. All logos and trade names are the property of their respective owners.