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Odd problem with my kitchen mixer tap - the hot side mostly works fine, but now and then mysteriously delivers cold/lukewarm water, sometimes for a few seconds, sometimes for minutes.
Other taps in the house working fine.
Is this likely to be a backflow issue? We have mains pressure hot water, although the issue has got worse since I swapped out an isolating valve on the main supply for a proper stopcock with a bigger bore.
TIA...
Bump for the morning crowd.
Now tending towards the idea that the unvented cylinder may have a fault, as another of the mixer taps in the house seems to have a similar issue.
Tried to 'bleed' it this morning to check the expansion gap and I'm not getting the normal constant gurgling racket it makes while draining down.
Are you sure it's not heat transfering from the hot feed to the cold feed under the sink?
We get that occasionally, run the cold for a little bit.
Try a bit of pipe insulation between the feeds to check.
At a guess your hot water is at 3 bar off a un-vented cylinder and your cold is direct mains pressure which could be a lot higher.
Try shutting down the stopcock a bit and see if that helps.
Unlikely to be the cylinder, and also the pressure off the cylinder is likely to be higher than 3 bar as it is heated which will increase the pressure.
Could be a mixer tap or shower somewhere that is allowing water to mix, check the showers first. I've even had a pinhole in the brass casting of a shower cause that problem.
If you're on an unvented DHW cylinder, the cold water feed for your taps **should** tee off after the pressure reducing valve so as to keep hot and cold water feeds at the same pressure. Check where your cold feed comes from first.
Cheers all.
I did close down the stopcock a bit with no great effect, might have another go.
I'm having to swap out the shower for another reason in the next week or so anyhow. Wouldn't surprise me if this was the issue.
May have to get the tank looked at anyway because it didn't sound normal during my attempts to reset the expansion gap this morning.
If the pressure regulation valve is failing and allowing more than 3bar into the tank, could that cause any of the symptoms I've described, or would I just get very good hot pressure? 🙂
If you’re on an unvented DHW cylinder, the cold water feed for your taps **should** tee off after the pressure reducing valve so as to keep hot and cold water feeds at the same pressure.
Not sure, will check, cheers.
It's more likely that your cold taps are fed straight from the mains, which could be anything from 1 bar up to 6-7 bar, depending on where in the country you are and what the demand is like. If you have 3 bar hot water, 4-5 bar cold water and a mixer tap that mixes in the tap body/doesn't have check valves then you're likely just pushing higher pressure cold water up the lower pressure hot water pipes. The fact that it's intermittent could just be down to your mains water pressure bouncing around the 2.5-3.5 bar region.
Your PRV failing shouldn't cause cold water from the hot tap, but if it has failed and the cylinder is overpressured you should be able to see a flow of water through the little plastic tundish on the side of the cylinder.
Is it worth fitting a separate 3bar PRV on the mains feed just past the stopcock, while I've got access?
You could, but I wouldn't. It's just one more thing to go wrong. Simplest fix would be to change the mixer taps you're having trouble with. Get something that keeps hot & cold separate and only mixes at the spout. No chance of backing up inside the tap body then.
Has this issue only recently started? If so, I would look for the simplest possible cause and that of the mixer tap itself.
Ceramic cartridges for hot and cold? Or rubber washers? Or as mentioned above, a crack or hole in the internal casting which allows more cold water into the mix.
IANAP, however if it’s just started, I doubt you need to start looking at the complications of pressure balancing, PRV’s yadda yadda yadda. 😁
I’m having to swap out the shower for another reason in the next week or so anyhow. Wouldn’t surprise me if this was the issue.
I've had a failed cartridge in the shower allow cold water into the hot side. It was easier to pin down as the hot tap it was affecting wasn't a mixer. Assuming you have isolating valves on the shower (and if not, fitting some would make swapping it easier), try closing them and see if the mixer tap problem disappears.
Unfortunately, no iso valves on the shower. In fact, the only reason we've got a new stopcock is that I found the existing valve, and another one supplying the bathroom had both seized solid when water started pissing out of the shower! My son learned some novel swear words though, so all good.
Thanks for all your help. I have something approaching a plan now. I've turned the new stopcock down a bit more and it seems to have helped a bit.