Getting hot water from shower to actually be hot

[jgharston]

Grrr. This is why I prefer proper stored hot water systems...

My shower has a mira Discovery thermostatic mixer, one of these:

Try as I might I can't actually get the hot water to be hot. With the temperature control turned all the way to "hot" it just runs tepid, I end up shivering when trying to have a shower. Following the instructions I've turned the internal temperature control adjuster within the green temperture hub, I've ended up turning it so far the worm scren is starting to poke out of the hub, yet it *STILL* runs cold.

Basin mixer tap runs nice and hot, kitchen mixer tap runs nice and hot.

Any advice?

At the place I used to live I had 25 gallons of hot water sat waiting for me instantly onstandby.

JGH

[jgharston]

Sorry, no, actually one of these:

[jgharston]

PS: Boiler is a oil-fired Warmflow Combi 90, serviced in June.

JGH

[nicknoxx]

If the water is hot at the sink then it's not the boiler or the system. It must be the shower mixer. I've had one of those showers and it was fine. Has it ever worked? Are the hot and cold supply fitted correctly? Is there a blockage in the hot supply? If you stop cold water reaching the shower does hot water come out?

[jgharston]

Not since I moved in in May. It's only now getting annoying as the weather gets colder.

Dunno, can only presume that the person who built/plumbed the house last year fitted them correctly.

Hmm. That would be an interesting experiment, though how I would do it without ripping out the wall on the other side of the shower or breaking up the concrete floor I'm not sure.

JGH

[nicknoxx]

Hmmm, looks like you'll have to have the shower mixer off the wall then

[Andy Champ]

Turn it half way and stick your hand under it. Then turn it up gradually and feel what happens. Then report back!

Andy

[jgharston]

At halfway, runs at 37degrees. After 30 seconds turned up to full hot. Continued running at 37 degress.

JGH

[jgharston]

Hot water in the basin runs at 47 degrees.

JGH

[John]

Can you check the temp at a tap whilst the shower is running? You may be 'blaming' the shower when it is the boiler that is lacking capacity.

I have a Mira 415 and I needed to fit a flow reducer in the winter to allow the boiler to cope - it was delivering 12 litres a minute and the boiler struggled. It is now 9 litres a minute and it is fine

[John]

I realise now that your has a "flow" control (mine doesn't). Is the problem there at lower flow rates?

[Gib Bogle]

Possibly the pressure in the hot system is too low. We had a new cylinder installed recently and at first the pressure was too low - hot water in the basins, but the shower mixer dropped the flow right down. The plumber came back and cranked up the pressure reducing valve (whatever it's called), and now it's fine.

[jgharston]

There's no cylinder, that's what's annoying. I'm used to a cylinder with 25 gallons of hot water sitting there waiting for me to use it at any time, not waiting for a boiler to suddenly wake up and desperately try to heat the water as it rushes past it.

That might do it. I'll have a chat with the landlord (or see if I can find it myself).

JGH

[John]

Trace the pipes - do you perhaps have mains cold on one side and gravity hot on the other?

[Dave Liquorice]

Good test and I'd go with lack of capacity in the boiler especially as it's only since the supply started getting colder that the problem has appeared. Another thing is the OP not finding a "safety interlock" that prevents the shower going above 38C or 43C (ie cold to tepid) unless defeated. Though it doesn't look like this one has such a "feature".

[Owain]

Perhaps you may feel that some of their other products are apt?

thought of a combi boiler deters me from turning the tank cupboard into a useful cupboard.

Owain

[The Natural Philosopher]

Its combi dear.

There is no 'hot water' system as such.

[Dave Plowman (News)]

It seems to be designed for either low or high pressure systems. Assuming yours is high pressure being a combi perhaps the cold flow is too great for the mixer to compensate for? You could prove that quite easily by cutting it down on the main stop c*ck.

[jgharston]

Don't want to dig up the concrete floor or bash holes in the stud walls.

No, it's a combi with no cylinder - ie mains cold, mains hot.

JGH

[jgharston]

Yes, that heats it up. However, it also cuts the flow (!) just as I've always experienced with non-stored systems. You throw away water flow in exchange for heat, and the cross-over point is always too crap for either.

It just manages to get up to 44 degrees with water running out at a trickle. Proper decent pressure gives a temperature of 35 degrees, brrrr!!!!

Just after the stop-tap there's an inline connector with a nut on the side that I've never seen before, looks a bit like this:

is a new-build house in Aberdeenshire, it's about 18 months old.

JGH