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
--
Please don't feed the trolls

Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload
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
--
----- -
This newsgroup posting comes to you directly from...
  Click to see the full signature.
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload
On Thu, 18 Jan 2018 08:40:56 -0000
<in the voice of Andy Parsons> Ooh you naughty person, you've got that set too hot, you're going to scald yourself.

Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload
On 18/01/2018 07:47, Tim+ wrote:

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.
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload

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
--
Please don't feed the trolls

Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload

Is the boiler shutting down - a simple observation.
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload
On 18/01/2018 09:31, Tim+ wrote:

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?
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload
GB wrote:

The flush-mounted Mira ones remain accessible after tiling, just an easy to pull-off faceplate and you can replace the cartridge.
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload

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).
--
Today is Pungenday, the 18th day of Chaos in the YOLD 3184
Ph'nglui mglw'nafh Cthulhu R'lyeh wgah'nagl fhtagn.
  Click to see the full signature.
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload
Huge wrote:

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 ...
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload

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.
--
Today is Pungenday, the 18th day of Chaos in the YOLD 3184
Ph'nglui mglw'nafh Cthulhu R'lyeh wgah'nagl fhtagn.
  Click to see the full signature.
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload
On 18/01/2018 12:15, Andy Burns wrote:

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.
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload
dennis wrote:

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.
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload
On Thu, 18 Jan 2018 07:47:26 +0000, Tim+ wrote:

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
--
AMD FX-6300 in GA-990X-Gaming SLI-CF running Windows 7 Pro x64

Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload
On Thursday, 18 January 2018 11:18:17 UTC, David WE Roberts (Google) wrote :

tarting

s
o fix it, all

tried turning it

re are no

e

t

.
Or just set the shower to a higher flowrate to avoid boiler shutdown. Combi s can force water & gas waste this way.
NT
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload

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
--
Please don't feed the trolls

Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload
On Thu, 18 Jan 2018 16:17:36 +0000, Tim+ wrote:

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..
<https://forums.digitalspy.com/discussion/1805261/can-only-get-hot-water- by-turning-up-heating> 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".
<https://www.superwarm.co.uk/troubleshooting-combi-boiler-faults-water-is- lukewarm/> suggests it may be the hot water thermistor.
<https://www.superwarm.co.uk/ultimate-guide-to-diagnosing-a-faulty-boiler- diverter-valve/> 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
--
AMD FX-6300 in GA-990X-Gaming SLI-CF running Windows 7 Pro x64

Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload

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
--
Please don't feed the trolls

Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload
On 19/01/2018 15:33, Tim+ wrote:

Good luck. I've had some right problems with BG servicing. 90% chance they'll try to sell her a new boiler.
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload

Very probably but as it’s only 5 years old, I don’t think my mother would fall for it. ;-)
Tim
--
Please don't feed the trolls

Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload

HomeOwnersHub.com is a website for homeowners and building and maintenance pros. It is not affiliated with any of the manufacturers or service providers discussed here. All logos and trade names are the property of their respective owners.