Shower not heating up - boiler fault?

KenDFish

We have an upstairs shower that has suddenly decided that hot water isn't it's thing. The water doesn't get beyond lukewarm at best - the temperature doesn't vary much; it gets slightly warmer after it's been ran for a few minutes both nothing like the piping hot water we used to get even a couple of weeks ago.

Both the shower unit - with a Mira MiniDuo mixer tap - and the boiler, a Worcester Bosch 37CDi, where installed around the same time, 14 years ago. The boiler has been regularly serviced, most recently about 6 months, and isn't giving us any other obvious problems - raidiators are fine, and all hot taps (including the one in the same bathroom) give out lovely hot water.

Having Googled about, the most common fault appears to be with the cartridge within the mixer tap itself. I've taken the front knob off and fiddled around with the "temperature control" using an Allen key - all to no avail. However, there's a couple of factors that make me think that this might not be the root cause:

• Having followed the advice on this video, the hot side of the "inlet elbow" isn't very hot - it's not something I paid much attention to before, but I'm fairly certain that this was red hot previously. I'd have thought that the hot tap being fine would suggest that there wasn't a problem with the hot supply; however, further on in that video (at 3m 40s), the chap says we can disregard the hot top as the flow rate is different.
  

• We have another shower in the house that is rarely used; however, I've tried that and it's not really much better. It does get hotter, but it takes AGES to heat up.

Given the above, does it seem more likely there's an issue with the boiler, or with the shower(s) themselves? We have "home assist" style cover on the boiler (with a small excess to pay) - would this likely fall under the category of there being a boiler fault (as opposed to just-not-working-very-well-for-one-particular-thing), and therefore something we could ask them to fix?

FreeBear

Are you getting hot water out of any other taps in the house ?

If you are, the problem isn't with the boiler.

KenDFish

FreeBear said:

Are you getting hot water out of any other taps in the house ?

If you are, the problem isn't with the boiler.

Yes - from my original post, "all hot taps (including the one in the same bathroom) give out lovely hot water". However, from that video:

"However, the thing you need to check first that there is the hot water supply to the shower and the way to do that is to grab the inlet elbow of the shower, or indeed if you can if you can't get that get the pipe that leads to the shower or and get the pipe that leads from the boiler to the show if that pipe is too cold or going hot and cold then the problem is more likely to be with the boiler that with the shower - the shower can only actually deliver what the boiler is giving to it.

Sometimes people will say, 'ah, all but the temperature of the taps are all
OK'; well you need to disregard the temperature of the taps because the tap has a different flow rate to the shower"

I guess my question boils down to (sorry): is he right - can I disregard the fact the taps are OK, and why wouldn't the "hot inlet" be hot any more?

grumbler

If the mixer valve is faulty and hot water flow rate is very low as a result, the hot water inlet can remain 'not very hot' just because the metal that the mixer tap is made from is too good heat conductor.

It's better, if possible, to check some more remote part of the HW pipe and give enough time for hot water to reach this part.

KenDFish

Afraid there's no way to get at the hot pipes, it's all behind the wall So, on the evidence presented, it's likely to be a problem with the cartridge within the mixer tap, and it's a job for a plumber?

grumbler

KenDFish said:

and it's a job for a plumber?

If you ask, then, possibly, yes.

macman

Hard water area, cartridge scaled up?
If you can isolate the supply, and do basic DI, then changing the cartridge yourself is a very simple job.

KenDFish

Soft water area I'm afraid. I'm ALMOST confident enough to replace the cartridge myself, but as they appear to be £100+ each and I'm not exactly sure what I need (which inevitably will lead to be buying the wrong model), it's probably something I'd feel safer paying someone to do.

ThisIsWeird

It's always going to be a bit of guesswork, but as Grumbler says, if the thermostatic cartridge is faulty (and they do go at regularish intervals) so that it doesn't feed much more than a hot trickle into the valve, then I wouldn't be surprised if the hot side of the shower would just be luke warm. So I'm not sure that video's test is a reliable one. 

Since you have a combi, the pressure from the H&C should be very similar, and the flow not a million miles apart either, so what happens if you turn on the 'flow' to max, and then move the temp lever full to H and then C and back again - how do the respective flows compare?

Replacing the thermo cartridge - usually the guilty part - is usually pretty straight-forward, and there's bound to be videos to assist.

Norman_Castle

This suggests checking the filters before replacing the cartridge. https://support.showerspares.com/support/solutions/articles/77000483128-common-problems-with-mixer-showers

Norman_Castle

KenDFish said:

• We have another shower in the house that is rarely used; however, I've tried that and it's not really much better. It does get hotter, but it takes AGES to heat up.

Long uninsulated hot pipe feed?