Please help - My boiler keeps turning itself off while I'm in the shower

ColdShowers456

Hi all, I'm hoping for some help please with an issue that's been troubling me for months.

As preamble, I have zero experience with DIY/home improvement so I'd really appreciate some advice in terms a dunce like myself can understand.  I live in a flat in a tenement block.  I have an old boiler, which is an Ariston Micro Genus 23/27 MFFI according to the instruction manual. No idea what make my shower is, it isn't branded.  All these fixtures were there when I moved in about 10 years ago, I haven't replaced anything to do with the water in my flat aside from my bathroom tap maybe 1-2 years ago which predates this issue by a signifiacant margin. I own the flat.

For maybe the last 6 months, whenever I take a shower the water runs cold after a few minutes.  I've run my shower with me watching my boiler and it's because my boiler turns itself off while the shower is running. I can also hear this happening in my shower room.  The boiler eventually comes back on and keeps heating the water after it seems to cool down completely, but this takes a few minutes and it's ice-cold for that time.  In addition, my shower with the right water aperture selected used to run with high enough pressure to strip the paint off an oil tanker.  It was fantastic.  Now it feels like it's down to a fraction of its previous strength which makes it much harder to wash the shampoo out of my hair.  It isn't a 'trickle', but it's definitely much worse. 

I've spent probably hundreds in plumber's fees to look at my boiler over the past couple of months but he's been no help.  My boiler has been losing pressure, with me needing to top it up maybe every couple of weeks.  I haven't ever needed to do this more than a handful of other times for my stay here, and never this regularly.  Therefore there is definitely something wrong. The plumber has looked at the pipes on the outside of my tenement and can't really see any so can't determine if there are any leaks out there.  None of my neighbours have commented/complained on leaks coming from my flat, so we don't think there's anything leaking inside my place that I can't see. He's replaced the expansion vessel and temperature sensor in my boiler and shot some anti-leak stuff into my kitchen radiator earlier this week, and my shower this morning seemed to go colder even faster.  The boiler pressure still looks to be falling.

What is strange, however, is this doesn't happen if I run the other taps in my flat.  They stay hot indefinitely, no boiler shut off, and seem to run as high pressure as they used to.  Consequently a way for me to "hack" this problem is to keep a hot tap on while I shower, which keeps the boiler from turning off and lets me have a hot (albeit even lower pressure) shower.  This suggests to me and my plumber that it might be a problem with my shower's thermostat.  But, the lack of pressure as I run the shower also suggests to me that it's a problem with my boiler or hot water distribution system.

Even stranger, very rarely the shower just works fine.  I've had one or two showers which have been high pressure and not run cold at all after 15-20 minutes.  I obviously have no idea what could have caused this - I wasn't running my heating or any taps, or anything to do with my water at the time as far as I can recall, though these happened months ago so I can't say for definite.  That suggests, to me at least, that the problem can be fixed without fully replacing anything.

I'm aware my boiler is ancient and is apparently a bad make, so I expect this will need replacing and can make my peace with that.  I'd prefer to avoid having my shower replaced as that will probably entail my bathroom being opened up.  Can anyone please give me some ideas I can try or suggest to my plumber short of replacing my boiler/shower? Or is everything here indicating these need replacing, and if so is it clear which is the culprit?

Brie

We had a similar problem where we used to live that was eventually (18 months later?) fixed by getting a new boiler.  

What we discovered was that the shower was fine at first but if the combi boiler turned on because heat in the house was required it seemed to prioritise that to heating water for the shower.  Like you there was no problem with getting enough water to fill the kitchen sink or wash one's face.  I guess that was less of a stress for the boiler.  But in the shower if would warm up as normal, run for a couple of minutes and then it was just cold water.  I got very quick at showering.  

So our solution was before getting in the shower switching the boiler from heat and water to just water.  So it's only job was to make sure I had a hot shower.  Eventually come summer and the heat wasn't on at all it wasn't a problem but come the autumn it all kicked off again.  Things eventually escalated that we couldn't get hot water at all anywhere and that's when we got the new boiler - it was lush!  

You may want to consider this as your ultimate option and aim for having the new boiler installed in the summer when there might be less call on boiler working types are potentially less busy.  We didn't time it right so ended up with no hot water for a couple of months at least.  As it was I ended up having to go to the gym every morning before work just to shower so I'd be both awake and clean.  

ThisIsWeird

Hi CS.

A combi that runs cold and then comes back on, and keeps cycling like that, usually indicates a partially blocked secondary heat exchanger. However, you are also experiencing a drop in flow through the shower, and the hot runs fine when drawn through a tap, so this would more likely point to the shower unit.

Photo of the shower, please?

When you turn the temp control to cold, does it now flow with force?

daveyjp

I'd start with measuring the water flow rate.  Cold water at a kitchen tap.  Time how long it takes to fill a 2 or 4 litre container.

barbuda

Hi,
Sounds as though the shower has a built in thermostatic control that is intermittently faulty.
It thinks it is hot when it isn't, so it restricts the hot water because it thinks it doesn't need it. The boiler then shuts down as it doesn't detect a demand for hot water.
If the pipes to the shower are accessible, disconnect the hot water pipe to the shower and let the pipe run into a bucket, if there is a good flow of hot water then the shower is faulty.
If the shower is on a plasterboard wall then there may be access to the pipes in the room on the other side of the wall...
Failing that a replacement shower cartridge (if available) or a new shower seems to be the way to go.

Ectophile

A combi boiler requires a minimum flow of water through it when heating.  if the flow is too low, the boiler shuts down to avoid overheating.  Once it's cooled down, it may restart again.  It looks like your boiler is rather old, and maybe it can't modulate down (i.e. turn the gas down) when the water flow is less.

You should investigate why the flow through your shower is lower than it should be.  That could be as simple as a build up of limescale in the shower head, or possibly furred up pipes or a faulty thermostat.

If the boiler works normally when running the hot tap, then it's probably not the boiler that's the problem.

Rodders53

Shower mixers often have non-return valves and small mesh filters that need checking/servicing/cleaning.  If they are clogged (or NRV not opening fully) they will slow the HW flow then you'll have that sort of issue.

Isolate H & C to the shower mixer and remove / clean? 

Any plumber worth their salt would have know that, though.

Mr.Generous

ThisIsWeird said:

Hi CS.

A combi that runs cold and then comes back on, and keeps cycling like that, usually indicates a partially blocked secondary heat exchanger. However, you are also experiencing a drop in flow through the shower, and the hot runs fine when drawn through a tap, so this would more likely point to the shower unit.

Photo of the shower, please?

When you turn the temp control to cold, does it now flow with force?

I've had exactly this, it was the heat exchanger. On an old boiler in a rental, best bet was a new boiler. Fix this then sort next problem out a couple of months later ...

ThisIsWeird

Mr.Generous said:

ThisIsWeird said:

Hi CS.

A combi that runs cold and then comes back on, and keeps cycling like that, usually indicates a partially blocked secondary heat exchanger. However, you are also experiencing a drop in flow through the shower, and the hot runs fine when drawn through a tap, so this would more likely point to the shower unit.

Photo of the shower, please?

When you turn the temp control to cold, does it now flow with force?

I've had exactly this, it was the heat exchanger. On an old boiler in a rental, best bet was a new boiler. Fix this then sort next problem out a couple of months later ...

It doesn't really fit in with the OP's symptoms, tho'.

DRP

Non return valve would be my guess. 

ThisIsWeird

CW456, you appear to have two separate issues with your boiler, and they aren't necessarily connected.
The first is your cycling, and low-flow shower. To help further, we need a pic of your shower mixer (and some willingness for you to do some basic DIY plumbing).
And then there's your system pressure drop. To help with this, we need you to be able to look at two pipes that are presumably existing your flat's external wall, one thing copper, and the other thicker white plastic.can you see these?
Or, alternatively, we could try isolating your boiler from the rest of your system for a day or so, and that should help narrow down the source. For this, we need a pic of the underside of your boiler, where all the pipes come out.