Combi/shower problem

My mother?s shower is playing up. Apparently it has taken to starting off fine but then going cold after a couple of minutes.

I went up and had a look and as far as I can make out, the boiler seems to be behaving normally when you run a hot tap. Even at relatively low flows it kicks in and starts heating the water. The problem only happens with the shower.

It?s been looked at by a plumber who hasn?t been able to fix it, all he?s done is to crank the boiler temp up to max. I?ve tried turning it back down but this hasn?t helped apparently.

I don?t know what kind of mixer valve the shower has (whether thermostatic or pressure balancing) but irrespective of this, it *used* to work fine and now doesn?t. The shower head is clear and there are no obvious obstructions.

Any thoughts? My mother is getting rather fed up with it.

Tim

Reply to
Tim+
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Are we definitely sure its fed from the hot and not self heating? My guess is that there is a thermostatic mixer fault.

I don't know enough about these myself but most showers seem to have protection against them going so hot they can burn and scold people. Brian

Reply to
Brian Gaff

Thermostatic mixers do go wrong. Especially in hard water areas.

I take it that this isn't a nice surface mounted shower mixer - the type with two tails permanently fixed to the pipework? That takes around two minutes to replace, which aids problem solving no end.

Reply to
GB

It?s a soft water area (Glasgow). I know theostatic ones do go wrong but I thought pressure balancing valves were the preferred option for combis? At present anyhow, I don?t know what kind it is.

No such luck alas.

Tim

Reply to
Tim+

Is the boiler shutting down - a simple observation.

Reply to
DerbyBorn

One suggestion - run the hot tap at the same time to ensure the boiler is still firing.

Then see if the shower runs warm then cold.

As DerbyBorn suggests, first check if the boiler is shutting down (although, thinking about it, if the mixer is only running cold then the boiler will be shutting down anyway).

This should tell you at least if it is too low a flow through the hot side of the mixer to keep the boiler running or if the mixer just won't let hot water through once it gets up to temperature.

Either way it looks like a new mixer, or at least a replacement cartridge.

As far as I know with a combi you can have a manual mixer or a thermostatic one as both feeds are at mains pressure. I prefer a thermostatic one for general safety and lack of fiddling. If it is thermostatic there should be a numerical temperature scale on the temperature control, and probably a red button as an interlock to stop it being turned up too hot by accident.

Cheers

Dave R

Reply to
David

o fix it, all

tried turning it

Or just set the shower to a higher flowrate to avoid boiler shutdown. Combi s can force water & gas waste this way.

NT

Reply to
tabbypurr

Luck should not come into it. Why do people bury stuff like this in the walls? Hopefully, you can fix the mixer with just a new cartridge. You didn't mention the make or model.

Have you tried running a hot tap at the same time as the shower, to see whether that helps?

Reply to
GB

The flush-mounted Mira ones remain accessible after tiling, just an easy to pull-off faceplate and you can replace the cartridge.

Reply to
Andy Burns

One of the joys of so-called "digital" showers. The plumbing is all easily accessible (assuming you put the pump/mixer unit somewhere you can get at it.) There's no plumbing in the shower cubicle other than the shower head(s).

Reply to
Huge

Hadn't appreciated there were any like that. Still I bought all the mixer/diverter valves and new heads for my bathroom refurb over a year ago ...

Reply to
Andy Burns

I withdraw my recommendation. Not an hour after posting that, the damn thing threw a wobbly. I had wet and soaped my hair, switched it off while I lathered and then the damn thing wouldn't switch back on. Having washed the shampoo out of my eyes in the wash basin, the remote control is showing an error icon which I believe means "Cannot communicate with mixer unit". So I stamped, naked (ick), wet, soapy and cold (and very, very, very angry) down to the guest bathroom and finished my shower in there, which sadly has another MIRA digital shower in it.

What's worse, having powered the mixer/pump unit off and on (once I'd calmed down), it's fine, so there is no fault to find. Grrrrr.

So now and forever, it's going to be a lottery whether the damn thing is going to work properly or not.

Reply to
Huge

Well yes. ;-)

Anyway, I?ve been back up to Glasgow to do more tests. Part of the problem is that it seems to be intermittent.

For reference, it?s a Triton Eden concentric thermostatic mixer linked to a

5 year old Worcester Greenstar 28i combi boiler (recently serviced).

First I ran the shower. Of course it worked perfectly providing lots of controllable hot water, as did the hot taps.

After a bit of thought I realised that the CH was calling for heat whist I had been testing it so I cranked the stat down and this time both the shower and the hot taps would only produce tepid water (never ice cold which is the problem that my mother has been having).

I watched the boiler whilst I turned on the shower and hot taps and with the CH off, the boiler would fire up appropriately but would only produce tepid water. After turning the wall thermostat up to ensure that the CH was calling for heat, I could get scaldingly hot water from the hot tap again and the shower seemed to work okay.

I was completely unable to recreate the fault whereby the shower suddenly goes cold but clearly something isn?t right with the boiler. Diverted valve maybe? Never owned a combi so not much experience with them.

Any thoughts? If it is the diverted valve, how easy is it to change one? Access is pretty good.

Tim

Reply to
Tim+

Its probably better and cheaper to get mira to do a fixed price service. They replaced all the internals on mine for £159 and the parts were over £400 on shower doc.

Reply to
dennis

Touch wood, mine has been pretty good, a couple of years after installing, it wasn't regulating temperature properly, so I replaced the cartridge, could well have been my fault for letting some flux or grit get in during install.

Since then (a good 20+ years) not a peep from it, it has had two new hoses and one new head, that's all.

I have got a replacement lined up, and I didn't go with a Mira because their "eco" head can't cope with the full flow from my pump, it pisses water out from every seam of the head, and they don't do a mixer with dual outlets.

Reply to
Andy Burns

Well, at least you now know that it probably not the shower which is the main fault - although that doesn't mean that the shower is fine, just that the first order of things is to get hot water coming out of the taps.

From your tests, I would be looking sideways at the plumber and wondering why s/he couldn't work out that there wasn't piping hot water to the taps when the CH is off.

It sounds as though the boiler just isn't firing up enough when the hot water is running - heat exchanger seems fine because you do get piping hot when the CH is on.

I wonder if it is the thermostat for the hot water side? Never delved into the innards of a combi but AFAIK it can only serve hot water or CH so something on the CH side must be keeping the water temperature up when the CH is on but you are serving hot water..

suggests faulty diverter valve, as do you. However some of the posts go on to talk about 3 position valves and head units which sounds more like a stored water system.

From what I read about the diverter valve this makes me think that the "no hot water to taps" means "no water to taps" not "warm water only to taps".

suggests it may be the hot water thermistor.

looks useful, as well.

The fact that you get warm water with the CH off makes me think it is more likely to be the thermistor but I'm just getting.

Pray it is the thermistor because that seems to be a lot cheaper and easier to fix!

Cheers

Dave R

Reply to
David

That's interesting. In your OP, you said "the boiler seems to be behaving normally when you run a hot tap. Even at relatively low flows it kicks in and starts heating the water. The problem only happens with the shower."

There's no rush to get this fixed. Just tell your mum to turn the CH stat up before having a shower. ;)

Reply to
GB

Ooh you naughty person, you've got that set too hot, you're going to scald yourself.

Reply to
Rob Morley

I think the problem was that my mother contacted her plumber who fitter her shower rather than about about a boiler problem.

I?ve since established that she has a BG Service contract and they?re coming out to look at the boiler today. Fingers crossed they sort it.

Tim

Reply to
Tim+

Good luck. I've had some right problems with BG servicing. 90% chance they'll try to sell her a new boiler.

Reply to
GB

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