Hot water coming out of cold water taps

[Spanky2k]

We've had this issue for as long as we've lived here i.e. for most of the year, when you turn on the cold tap, it'll run warm for up to a few minutes before cooling down. Unfortunately, with it being cold now and the central heating being on a lot of the time, the water that comes out the cold tap is now *hot*. As in, it's steaming. It takes about a minute at least to cool down. Not long after we moved in, we had three of the four bathrooms / toilets redone. There's one bathroom in the loft conversion that wasn't modernised. It has a mixer sink and a shower. The tap in the kitchen is new too. Our heating system is a boiler plus a hot water tank with an immersion heater. The immersion heater has never worked and is off (power switch supplying it is off).

From what I've seen online, I believe the most common cause of this is a faulty immersion heater being stuck on, which can't be the problem in our case as the immersion heater is permanently without power. The only thing I can think that it might be would be the shower mixer on the top floor but I can't isolate that (no accessible valves). I have tested the old mixer sink in this bathroom (it has tap valves accessible underneath it).

Is there anything else any of you guys can think of that I might be able to try first? The cartridge to the shower is awkward to get to so I'd rather exhaust all other options before ripping that out.

 

[stem]

when you turn on the hot tap, it'll run warm for up to a few minutes before cooling down.

Is that what you meant to say? based on the title of your thread i would have expected it to read "when you turn on the cold tap, it'll run warm for up to a few minutes before cooling down"

If so, moved into a house and had similar symptoms. The problem was that the cold water pipe had been run alongside the boiler pipes and when the heating was on it warmed up the water in the cold water pipe, which has to be discharged before it ran cold. I rerouted some of the cold pipes away from the heating pipes and insulated other parts, which resolved the problem. Whist the water wasn't quite 'steaming' it was very warm.

The immersion heater just heats the water in the hot water cylinder in the same way that the boiler does, so even if the immersion was on it wouldn't make any difference, as the boiler will be heating the cylinder anyway. Also, the cylinder will hold 100 litres or more so it would take a long time to empty it, before it ran cold.

If it doesn't happen when the boiler has been off for some time and the pipes cooled, that would be where I would look first.

 

[Spanky2k]

Sorry, yeah that was a mistake. It's hot water out of the cold tap. I originally thought it might be something like in your case i.e. badly placed pipes. However, if the boiler's been on for any length of time recently, it's scaldingly hot. Actually steaming, that's not an exaggeration.

 

[fezster]

Is there anything else any of you guys can think of that I might be able to try first? The cartridge to the shower is awkward to get to so I'd rather exhaust all other options before ripping that out.

Can you isolate your HW cylinder? Once done, you should get no water from your hot tap (or a dribble at most). If you have a faulty mixer valve, you'll get cold water coming out of your hot tap.

 

[Spanky2k]

Can you isolate your HW cylinder? Once done, you should get no water from your hot tap (or a dribble at most). If you have a faulty mixer valve, you'll get cold water coming out of your hot tap.

Unfortunately not as there are no valves on the hot pipe coming out of the top of my water tank. However, that is a good call as the pipework around the top of the hot water tank, while not super accessible, is a lot easier to get to than the shower mixer so I could drain the tank and put in a valve relatively easily.

 

[EFLImpudence]

You turn off the cold feed to the bottom of the cylinder.


You haven't said but does the hot tap behave as it should?

 

[JohnD]

eeeeeek!

What colour is your hot-water cylinder?

Do these "cold" taps, that are running hot, deliver water from the mains, or from the cold tank in the loft?

The way to check, put your thumb over the spout and turn the tap on. Can you stop the flow of water with your thumb?

Yes = tank

No = mains.

If tank, climb up into the loft and see if it is cold, as it should be

Check the loft taps as well as they may be plumbed differently. If so, are they also hot?

 

[terryplumb]

Sorry, yeah that was a mistake. It's hot water out of the cold tap. I originally thought it might be something like in your case i.e. badly placed pipes. However, if the boiler's been on for any length of time recently, it's scaldingly hot. Actually steaming, that's not an exaggeration.

Does the problem exist on EVERY cold tap or certain ones ?

 

[Nozzle]

Do you have any mixer taps or a thermostatic shower?

Nozzle

 

[Spanky2k]

I'll try to answer everyone's questions!

As far as I can see, there's no way to turn off the cold water tank just on it's own. The hot taps all behave as they should. As far as I understand it, the hot water system is mains water driven i.e. it uses mains water pressure to push the hot water until it's cold. It's not a low pressure system. There is no tank in the loft and the hot water tank is in the cellar. Every cold tap in the house behaves the same way i.e. a splash of cold, then through to very hot and after a minute or so, back to cold. I *think* the go hotter faster (i.e. less initial cold water) the further they are from the boiler i.e. the cold sink tap in the loft conversion takes a few seconds extra before it goes super hot although they all seem to take just as long to cool down. I think this suggests the issue is not with the loft shower thermostat as if it were, I would expect the sink tap up there to go hot fasters. It's hard to tell though. The water tank is a white Megaflo.

We have 3 thermostatic shower units in the house. One is the ancient en-suite in the loft which is the most likely source of a problem if it is faulty thermostat related, one in the main bedroom en-suite (newly installed Grohe unit about 2 years ago) and one as part of the family bathroom's bath (also a newly installed Grohe unit about 2 years ago). The taps are all mixer taps in the house, all of which have been newly replaced in the last two years apart from the loft bathroom's sink, which I've already isolated and have ruled out (not that it's thermostatic anyway).

 

[terryplumb]

You have an unvented cylinder and pressurised system .The cylinder should be serviced annually , has it ?

 

[Spanky2k]

No, it’s not been serviced as long as we’ve lived here and the house was unoccupied for about a year before we moved in.