Shower not heating up - boiler fault?

plumb1_2

I would check the filter is not blocked before ordering a cartridge, plus sometimes the small non return ball/ plate sometimes sticks, check that’s moving freely 

macman

To buy the cartridge, you just need to identify the make and model of your mixer shower: there's only one cartridge.

ThisIsWeird

KenD, are you up for removing the cartridge yourself? There are loads of videos, many by Mira themselves, and it's pretty straight-forward, tho' with a few little things that might make a complete novice wary - such as circlips, setting the max temperature 'stop', etc, but it's all very doable with the instructions being followed carefully.

The 'trickiest' bit with yours is removing the large control handle - no idea how that comes off (but it will be quite straight forward once found out).

If you remove the cartridge - simply unscrewed using a largish socket - then you can not only try cleaning it, bit can check the H&C flows to the shower, to eliminate them as the cause. Turn them on one at a time, and you'll soon see if the mixer is received a proper flow of hot - it'll gush out the open front into your shower.

You'll then know if it's a supply issue or pretty much the only other option - a new cartridge is required. Gulp, not cheap at around £130?

If there is obvious build-up on the existing one, then a good soak in vinegar or scale remover might do the trick. Turn the cartridge to a different setting every hour or so. 

Are there isolating valves for the mixer? If not, that'll make life a lot harder. Don't necessarily expect to find them in the room next door (where the pipes appear to go), but possibly in the loft above, behind the bath panel or cupboard in the bathroom. Really bad if none fitted.

ThisIsWeird

If your 'home assist' doesn't cover the actual shower, then I doubt it'll help. I don't see this as being a boiler issue. Always possible, but just no real evidence.

It would likely be a boiler issue if the temperature fluctuated hot and cold, or up and down. But it seems as tho' it can supply a steady hot flow?

tetrarch

I did a quick google search - this looks like yours:

Mira Miniduo Exposed Valve Thermostatic Mixer Shower Chrome

https://assets-smallimage.qssupplies.co.uk/QS-V52530_3_mn.jpg

and your can get a new cartridge from:

https://www.showerspares.com/spares/mira-miniduo

£124.05

Best of luck 

Regards

Tet

macman

Remove the cartridge, clean and descale. Flush the pipework. Refit and test. 
Nothing to lose. If no improvement, replace the cartridge.

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.

ThisIsWeird

Well, I didn't see that coming 😃

Pleased it's sorted.

macman

'Some sort of valve'? The diverter valve?