Cold Shower

[LMW1990]

We moved into this house 2 years ago. It's an old house but prior to us renting it, the landlord gutted the place so it has new everything - including boiler and central heating (the old lady who owned it before only had heaters).

The heating works fine. The boiler has been inspected etc. It has lost pressure twice but we topped it up and there was no problem.

Now, the hot water upstairs in the bath or shower has never been what I'd call boiling hot. It's hit and miss.

The kitchen tap gets red hot after a few minutes as does the bathroom sink.

Lately the bath gets hot sometimes but the shower is almost always cold. You sometimes get a blast of hot water but not long enough to enjoy or have a proper wash.

The shower is not electric. I think it's connected to the bath taps as you can't use both together. It has a single knob that turns on or off.

DP is playing potty about it and our LL is, let's just say, not on the ball. We went to an event 1 hour from home today and chose to go last night and stay in a hotel, what swung it for DP was the prospect of a hot shower (he had 3!!).

Any ideas what the problem could be before I entertain a plumber?

If when you turn the bath tap on the water always at least gets warm, so the boiler is obviously working, but not hot, then if you slow the tap down and it does get hot and all the other taps always work fine then there's nothing wrong with the boiler. But if it's a thermostatic shower, some aren't designed to go on combi boilers. If it's been like it since day 1. if it always used to work absolutely fine and has developed a problem, then it's most likely the thermostat cartridge in the shower.

That's on the assumption you have a combi boiler. If it's not a combi and you have a copper hot water tank, and the shower is connected straight from the bath taps, you could check to see if it is mixed pressures. This means mains pressure on the cold and tank pressure on the hot. If you put your thumb over the end of the tap and turn the cold on, if it is mains you should not be able to stop the water spraying out the side of your thumb. If it is tank fed you'll easily hold the water back. If cold comes from mains and hot from the tank, you'll struggle to get the temperature right at the shower. It may be possible to put a constant pressure governor on the cold if it is mains although this a bodge, to put it right correctly would be to run a new tank-fed cold pipe to the shower.

Thanks for such a detailed response!

It is a combi boiler yes and we think it's a thermostatic shower. You're right in that the taps get hotter when slowed down/ not on full.

So, this is die to the shower not being compatible with the boiler?

It has always been not red hot I'd say but it's getting worse/ we are noticing it more these days.

Could you have a safety feature installed on the taps?

We had one when we moved into our house this year. Water would only get lukewarm at best not roasting. Got a plumber out and turns out it was a safety feature to stop people burning themselves

Anyway, it was a super easy fix!

Oooh I suppose that's a possibility. Where was the safety feature located?

You say it's getting worse.

If it's worse in winter than in summer, this is normal with a combi (or an electric shower).

Let's suppose your boiler can heat ten litres of water per minute by thirty degrees C.

In summer the incoming water from the mains might be, say 15 degrees, so the bathtap will run at 45C

In winter, if the incoming water is, say, 5C, the boiler will heat it by thirty degrees, and it will be 35C.

Additionally, any cold water you mix with it will chill it more.

Hot water cylinders work differently. They still heat to the same temperature, but take longer in winter.

If you have a thermometer, measure the temperature of the hot and cold water at non-mixer taps.

The effect will be greater at a bath tap that delivers a higher volume of water, because, even in winter, the boiler can heat, say, 5 litres of water per minute to a higher final temperature than it can heat 10 litres.

True, it's also possible for thermostatically controlled mixer taps to go wrong, and for other mixer taps to allow cold water into the hot taps; but my first thoughts are "combi not so hot in winter" which is sadly normal.

P.s.

One other thing you can try, if it intermittently runs fully cold rather than not very hot:

Unscrew the shower head from the hose (as if you were going to descale it)

Does the water running freely from the end of the hose heat better than when it's spraying?