Mixer shower only runs cold...

[rickycusimano]

Hi All,

I wonder if someone might be able to offer some advice before I have to remortgage my house to call in a plumber.

We have a simple mixer shower upstairs (standalone, not a bath) which has worked fine for months and now won't run hot water. We have a "Worcester 28i Junior" Boiler, and both central heating and all taps run both hot and cold water fine. I haven't touched anything, honest!

The mixer unit is very small, just has 2 'nobs' on, one for flow rate and one for temperature. There are 2 pipes running off it into the wall (a stud wall) straight up into the loft, along the floor about 3 meters then straight down, past the boiler and downstairs. The cold pipe joins the boiler, the hot one doesn't appear to (at least not above floor level). There are no obvious pumps or anything anywhere else in the house, I've even dismantled the bath downstairs.

When I open up any hot water tap, I can hear the boiler start up and a power light comes on. But when I turn on the shower, the water pressure is really low and there's no action from the boiler. Occasionally there is hot water for a minute or two, but the pressure remains low and it soon runs ice cold.

I've pretty much exhausted everything I can think of (not much) so any ideas would be most welcome.

Cheers

Rick

[John]

Are there some valves in the hot pipe. Sounds like something swelling in the heat and reducing the flow. I have a couple of stop taps in my loft to isolate the shower. Old washers can react badly to heat. Likewise it could be a similar issue with the miser - what make is it.

[rickycusimano]

The mixer doesn't have anything written on it... its shaped like a tube with the 'nobs' on either end, similar size to a kitchen roll tube.

I couldn't see any valves on the hot water pipe, and I followed the pipes as much as I could. There's a couple of valves on the cold water pipe... I haven't touched those since I moved in. The guy who sold me the house did show me those valves and said that if the pressure ever dropped, you just open those for a few seconds to raise the pressure. But the boiler has a pressure gauge on it and it doesn't seem to have dropped much.

Although its been hot recently we've had some cool weather the last few days and its still broken...

[john2]

are you in a hard water area ? I think the mixer is German/thermostatic and it could be seized up by limescale at the cold setting. As regularly happened to my succession of Mira mixers.

john2

[Owain]

Scale in the mixer is impeding the flow to such a point that the boiler flow sensor isn't operating?

Or a stuck washer in the mixer. If it was a tap I'd suggest a tap rejuvenator kit from plumber's merchant but don't know what the shower mixer equivalent is.

Owain

[rickycusimano]

If I had to put a date on it I'd say it started when we had the really hot weather about a week ago, limescale would have built up gradually over months and months wouldn't it?

How do I know if our water is 'hard' or 'soft'? Our kettle is fine, doesn't have any build up of limescale at all...

[john2]

probably very soft then, so ignore helpful comment. Sounds like the mixed is cream crackered for some other reason but could be something else. Focus used to sell them for £50 approx.

[rickycusimano]

Is almost certainly the mixer then? (ie the little unit hanging outside the wall?) And what do I do if I can't find one the same and the pipes are then in the wrong place?

How much would a plumber charge to fit a new mixer? Or is it something I should be able to do myself?

[john2]

From your description I think its one of these:

at £60 or at £100 which look very similar apart from price.

I would fix it if it was mine after messing with plumbing for 20 years or so. No idea what a plumber would charge (there must be plenty of plumbers around on this group who are staying stumm), but it's less than an hour's job if there are no problems. Get the H&C supplies turned off then the old olives and pipes should fit straight into the new mixer using the chrome nuts. If its the same type and pipe spacing that is. Check for dirt and damage around the olives and seating. And while the hot pipe is off, you could check that hot water comes through when it is turned on to make sure it's the mixer thats the problem and not further back in the pipe.

john2

[john2]

PS put a lot of old cardboard in the shower base in case a spanner or the mixer drops onto it, taking a chunk out (speaks from experience).

[rickycusimano]

Thanks for the advice guys

John the mixer is very similar to those two you pointed out only the nobs are more 'egg shaped' than either of those (not that I'm bothered, I'm just saying I dont' think its exactly the same)

Would there be any way of measuring the pipe spacing? I guess I'll have to go to a hardware store to measure them up. Though you'd think they could all agree on a standard...

[john2]

the pipe spacing on the screwfix ones is 150mm, or about 6" and more or less an industry standard, there should be enough slack in the holes in the wall for either.

john2

[Ed Sirett]

You say the water pressure is low? Has it noticeably reduced of late (we are in the middle of a drought a least in the SE half of the island which may be come of the problem.)

Can you measure some flow rates for the HW from the shower and taps?