Shower not heating up - could it be a 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, pressure is steady, 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?

 

[opps]

I am not a plumber...

If you open a hot tap on a basin, does the water get hot?

What kind of boiler do you have? Does it feed hot water to a copper tank or is it a combi boiler that fires up when you open a hot water tap?

EDIT- sorry, as per your mention of the boiler, you are on a combi.

 

[KenDFish]

Yes - hot tap is fine (but, as per that video I linked to, the chap suggests that might not be relevant). It's a combi boiler - so turning on a hot tap/shower causes the boiler to fire up and (in theory) give us hot water.

 

[opps]

If the water coming out of the basin or kitchen tap is hot, I would be inclined to think that the thermostatic valve in the Mira might be at fault.

Is the shower pressure OK(ish)?

I have heard that you can descale thermostatic valves, but that requires you to leave it in a bucket of descaling solution over night, and if you can't isolate the shower, you will have no water in the property over night.

a replacement cartridge isn't cheap though

https://www.mirashowers.co.uk/parts-accessories/shower-spare-parts/mira-pace-miniduo-adj-thermostatic-cartridge/

I guess another possibility might be crud in the hot water supply that is restricting the flow in the "strainer" rubber washer on the hot side of the valve.

Hopefully a proper plumber will be along soon

 

[HERTS P&D]

Just replace it for one of these:

Mulga Exposed Thermostatic Mixer Shower Valve Fixed Chrome - Screwfix

Order online at Screwfix.com. Exposed thermostatic bar valve with chrome-plated brass construction. Separate flow and temperature controls. FREE next day delivery available, free collection in 1 minute.

www.screwfix.com

Andy

 

[opps]

Just replace it for one of these:

Mulga Exposed Thermostatic Mixer Shower Valve Fixed Chrome - Screwfix

Order online at Screwfix.com. Exposed thermostatic bar valve with chrome-plated brass construction. Separate flow and temperature controls. FREE next day delivery available, free collection in 1 minute.

www.screwfix.com

Andy

Are the pipe centres/position uniform for all exposed mixers?

Edit- so you too think that the thermostatic valve is at fault rather than the combi?

 

[HERTS P&D]

Yes, the distance beteween the outlets is standard and if all the other hot taps are working correctly then it is the shower bar that is faulty.

Andy

 

[opps]

Yes, the distance beteween the outlets is standard and if all the other hot taps are working correctly then it is the shower bar that is faulty.

Andy

I suspected that might be the case, but thank you for clarifying it.

 

[denso13]

I think the mini duo has closer centres than the normal 150mm.

 

[denso13]

so you too think that the thermostatic valve is at fault rather than the combi?

Does it help with the basin and shower hot running at the same time? If not then it does sound like the shower.

 

[KenDFish]

Does it help with the basin and shower hot running at the same time? If not then it does sound like the shower.

Well just to add this into the mix (no pun intended):

- Bathroom hot tap when shower is switched off: water is very hot
- Bathroom hot tap when shower is switched on (and turned up to "hot"): water is lukewarm, as warm as the shower gets

Not sure if that helps, or changes anything?

 

[denso13]

Not sure if that helps, or changes anything?

Hmm possibly cold mixing with hot outlets when the shower is on. The easy option would be to try a different cheapo bar mixer but they won't fit your pipework.

 

[KenDFish]

Just to follow up on this, in case anyone has a similar issue: the problem was the boiler after all. We had an engineer out today, arranged via our boiler cover with the excellent YourRepair. He cleaned out the boiler (which, despite regular services, needed a lot of soot and general cruft removed) and replaced some kind of valve. We now have lovely hot water from the shower.

I'm glad I stuck with my gut reaction that there was something in that "Shower Doctor" video about not correlating tap temperature with the shower temperature: our boiler was capable of delivering enough hot water to keep up with the taps, but not with the much more demanding shower. The clue was the hot "side" of the elbows on the mixer tap - as I mentioned in the OP, they were lukewarm before - again, due to the boiler not being able to supply enough hot water.