Is there a boiler (house variety) engineer in the snug?

[oshodisa]

Hi all,

Our Combi boiler has an annoying problem which I wondered if anyone may be able to help explain.

Basically when showering the boiler keeps dropping in and out. This only seems to happen when it starts getting cold outside (i.e. in the last couple weeks/month).

It's not fun having to jump in and out of the suddenly cold stream when covered in soap!

The boiler is serviced every year by British Gas.

This doesn't seem to happen on any other taps in the house.

Anyone have any ideas as to what the problem may be and how it can be fixed.

Ta

 

[Shrek]

What sort of valve do you have on your shower? If you have one of them fancy temp controlling jobbies that it might be that it has a bit of cack in there and it is sticking and struggling to control the temp correctly. :hmm:

 

[oshodisa]

Hi

My shower (prepare for technical explination), has two pipes that go into it, a big dial that swings from red to blue and an arm that makes water come out of it!

:rofl:

being straight for a minute - is there an easy way to tell if it is a thermostatic mixer type or not?

 

[Crastney]

if there are two pipes coming in, then you have hot and cold inlet, and to start with the hot water entering will be cold (as it's in the pipe), then the boiler recognises that there is demand, and so it starts heating the water, and the hot water entering the shower gets hot. here's where it differes depending on shower type. I'm guessing that the temp control is basicall the flow of each side of water inlet, but the hot water starts cold, and then gets hotter, at some point the shower might realise that it's too hot, and cut the hot supply, hence the shower will go instantly cold, until the temperature control device cools down enough to allow more hot water to enter.

water pressure, and hence temp, can also be affected by usage of other taps in the house, especially if someone flushes the toilet, or the washing machine is on, or someone is filling the kettle.

my advice, if you can afford it, is to get a new shower, that only has cold inlet, which regulates the temp of the water leaving the shower unit regardless of the pressure coming in, so that should the pressure drop suddenly, the machine compensates, and uses less heat, so the shower water temp stays the same, but might go up or down in pressure.

that's what I think, but IANAP (I Am Not A Plumber)


[edit to add] it sounds from your description that there is not electricity involved with the shower itself, and it's just a mixer tap, so for some reason, the hot water supply is stopping, maybe because it's overloaded, running too hot, or other reasons as above - someone else using hot water supply. try turning the temperature of the hot water supply on the boiler down.

 

[markp]

I've just had the same problem with my combi.
There is a temperature sensor in the boiler that stops the water getting too hot and thus scalding the user.......when this starts to malfunction it just shuts the boiler down......I was constantly having to press reset to fire the boiler back to life.
Is this happening to yours??

Is it a boiler that shows error codes when it malfunctions?

 

[Shrek]

One way you can help fault find is to measure the temperature of the boiler out put while someone is in the shower. If the pipe coming out of the boiler is a steady temperature it would suggest to me that it is the valve. :hmm: Is it easy to remove the valve from the shower without detroying your bathroom? It might be worth running some descaler through it if you live in a hard water area. Where I live in Lincoln I have to descale my shower head once a month or you don't get wet. Still it is good for brewing bitters.

 

[oshodisa]

Crastney - as your edit points out, it is not an electric shower, the feed comes straight from the combi.

Regards resetting the boiler, we don't have to reset it, it just seems to cycle on its own. There are no error lights flashing (it's only got two lights which ahve a number of diff combinations to show different errors I believe)

Good suggestion re holding the pipe to see what comes out from the boiler and whether this is reflecting what comes out the shower. We live Loughborough direction and I don't think our water is overly hard although descaling the shower head etc would probably be a good idea generally as well.

The pipes run from boiler, under bath and up behind the wall, then exit through the tiles and straight into an independant mixer tap unit. I assume (will have to have a closer loko) that I must be able to peel off the front cover and get at the internals somehow. Although saying that - I've got form for breaking things in the bathroom - I once managed to break the toilet flush on Xmas eve by unscrewing it! Doh

 

[Shrek]

I would think you should be able to remove it without too much bother. Finding the isolation valves for it might be more interesting although I would think that any plumber worth his weight in copper would have put it behind the bath panel. Best of luck :pray:

 

[oshodisa]

isolation points are fun for that. I've previously taken the bath panel off for a leak.

One of the pipes has two isolators on it about a foot apart where the fitter obviosuly had different lenghts of pipe he needed to use up (pre us owning the house). I cannot remember the other!!

 

[pjbiker]

In my experience (not as a boiler engineer I might add). This type of fault is likely to be a cacked up 'Domestic Hot Water' heat exchanger. The boiler heats up water in its own closed circuit, which warms the water going to your shower via the heat exchanger, which coincidentally, is exactly the same as the 'plate chillers' many of us use to do the reverse.

When your cold feed isn't so cold in the summer, this works OK but now, the boiler's circuit temperature needs to be too hot to get your shower temperature up to the demand and keeps cutting itself out. The exchanger is probably cacked up with limescale. A replacement is usually around £100 plus fitting. However, if you want to have a go at stripping and cleaning it, a friend of mine totally fixed his by soaking it in citric acid he bought from his local asian grocer's.

Another common problem with combi boilers can be the 'diverter valve' which I have replaced myself before, but I suspect the DHW heat exchanger is your problem. I learnt about all this stuff by googling and looking on diy.not forum.

this kind of thing

 

[Phil_MG]

If you're getting a steady stream of hot water from any other tap in the house, then it's almost certainly the shower mixer/thermostatic valve that's at fault. It'll be wide open when you turn the shower on, as it warms up it'll be sticking and then closing suddenly instead of closing steadily as the heat of the water rises.

Best way to check for this is to turn on a hot water tap, slowly close it. If the boiler knocks off once you get to a certain flow rate and stays off then that'll point to the shower. If you close it slowly and it starts shutting off and then re-firing the boiler every 20 seconds or so and you're getting hot, then cold, then hot water then it's the boiler that's at fault.

 

[unclepumble]

It could also be a small hole in the diaphram of your expansion vessel, when this happens you will find you have to top up the circuit, every few months, (pressure guage drops) eventually you get equilibrium in the expansion tank, which can affect the flow switch.

Either that or the diaphram in your hot water pressure valve could be on its way out, (the diaphram valve that switches the boiler on when you run the hot tap).

If you pay British gas a payment to service your boiler get em out to fix it.

UP

 

[Shrek]

Any news? Is the house still standing?

 

[oshodisa]

Hi,

sorry for no weekend news - we were away (out of sight, out of mind!) but the house was still standing when we got back so that was good!

Anyway - got back late sunday and while in bathroom it sounded like teh boiler was struggling to fire while the central heating was on (no shower or taps running elsewhere).

was really to tired to investigate last night (guess what is on my list tonight!), but it sounded like a solenoid was cutting in and out, and the 'wumph' noise of the boiler lighting kept occasionally kicking in (then a solenoid noise, then a wumph again).

Looks like it may not just be the hot water feed, but the whole boiler is belly up!

All this and I had a single wall socket randomly stop working so I need to look at that as well - aargh old houses!!

Might be a case of getting British Gas out again (although it's only been a couple of months since it was 'serviced' - not entirely convinced they do a good job in the past!)

 

[Boomerang Bender]

Is the boiler oil fired or gas fired ?

 

[jasea3632]

I am a plumber/heating engineer and can categorically tell you that the problem is the shower mixer valve itself not the boiler others have stated that itcould be expansion vessel this can not be the case as when this happens as soon as your heating comes on the pressure will shoot up and blow off out the pipe that goes outside.
what is the age and make of shower???
The solenoid noise i presume is a fast clicking this is just the ignition and the wumph noise shows its lighting properly and not struggling to light as for constant cycling of off and on this could be caused by a poor siting of a room thermostat
hope this helps some btw most mixer shower manufacturers sell service kits so if you are told you need a new valve check first.