I've just moved into my new house which I've renovated, it's got a combi boiler and a standard shower, but the temperature seems to fluctuate quite a lot, basically the hot water keeps dropping out for a few seconds at a time, is this a trait of combi boilers, or do I just need to adjust something?

I think it might be a water pressure thing; combis need decent pressure. Have you got the stop tap opened fully?

if it's not a thermostatic shower it might explain the problem but when we had a combi and a thermostatic shower it was the best shower I've ever had – mains water pressure is great 🙂

Are you sure the shower is running off the combi boiler?

If not, the pressure drop when someone turns on the water can trigger the low flow sensor in the shower and it cuts power.

but the temperature seems to fluctuate quite a lot, basically the hot water keeps dropping out for a few seconds at a time

If it's a decent mixer with a thermostat – no. Does it do the same thing if you just run a hot tap?

It's just a mixer tap running from the mains http://www.focusdiy.co.uk/MinimalisticBathShowerMixer223449?category=bathroom_taps and no one else is turning a tap on.

We have a combi and a standard (non-therm) mixer. The water temperature is fine and constant unless someone turns on a tap/washing machine running/dishwasher running etc.

Unfortunately for us, the way the pipes are routed, we share a feed with five other properties too so if any of them turn a tap on….

But no – assuming you have a constant feed, the temperature shouldn't fluctuate.

Do you share a feed with other properties? Is the water pressure at the shower head dropping?

How would I know if I share a feed? I have got my own meter and can turn the water to my property off at that point so i would assume no.

The pressure did drop slightly at the head.

Sounds like a water pressure thing to me. check the pressure gage on the boiler, recommended pressure should be in the instruction manual. My boiler works best at 1.5 bar

Ok cheers, I will have a look at that.

How would I know if I share a feed? I have got my own meter and can turn the water to my property off at that point so i would assume no.

Imagine a hosepipe with feeders coming off it – at the end of each feeder there could still be a meter and a way of switching it off at the house (there SHOULD be a way to do that!) so you could still have a shared feed.

And when I say shared feed, I mean a smaller gauge pipe than the water main (because we are all on a shared feed from the main). Where is the stopcock? How many other houses does the stopcock feed? How old is the house? What type of house is it (terrace etc).

Your local water authority *should* be able to tell you.

I meant, run a hot tap with the shower OFF – do you still get a temp fluctuation from the tap water?

The pressure did drop slightly at the head.

And if it does that, the boiler will compensate to stop you from being Boil in the Bag Cornford

Each house has a stop cock just inside the front door.

It's an early 1900's terrace, 1906 I think.

Come to think of it when I was running the hot water for the washing up the water did go cold for a few secs and then run hot again.

Come to think of it when I was running the hot water for the washing up the water did go cold for a few secs and then run hot again.

Not the shower mixer then – as others have said, probably low pressure feed to the boiler.

I will have a play around with the pressure then and hopefully that will fix things. Thanks guys.

Each house has a stop cock just inside the front door.

It's an early 1900's terrace, 1906 I think
Is it a stopcock (ie, on the floor, little metal lid to lift) or just a tap inline on a pipe inside the house?

Also, some combis can take a minute or two to catch up with themselves once you switch on as the electronic gubbins works out what is going on and the water is flowing.

I'm not sure as it's underneath the laminate floor! I have got stop valves by ever appliance though. I have got what you describe outside my house.

I have got what you describe outside my house.

Then it *sounds* like you aren't on a shared feed then – I would *assume* the stopcock (outside your house) is coming from a mains pipe so you should have very good water pressure.

It is very easy to test pressure – your local authority will have instructions. Quite simply you need a bucket, fill it with a determined amount of water and time it. If it takes <time than the maximum allowed then you have acceptable pressure. If it takes >time then they may come out and carry out work UP TO your boundary for free. Any work inside your boundary is your responsibility.

Can you tell I have had recent issues with this yet… 😥

Yeah I could tell, all sorted now I hope?

Yeah I could tell, all sorted now I hope?

Nah – we live on an 'unadopted road' and the pipe from the main is shared between several terraced houses on the row (and runs under everyone's yards). As soon as the pipe leaves a publicly accessible place they aren't interested.

Hence we can sometimes have a trickle of water (much lower pressure than is acceptable under their terms) and it all is still lead piped in 2010!!!! Unless we pay someone (£ several thousand) to do the work on the private side (even though it means accessing at least five other people's properties) anything they do on 'their' side is useless. 🙁 So we make do with a Brita water filter and occasional rubbish showers (especially at going to work time).

Rusty Mac- don't confuse the pressure in the heating system (radiators) with the mains water supplying domestic hot water.
Combi boilers are vastly more complicated than normal ones and one of the things that wears out in them is the Diverter Valve: Inside this is a rubber membrane that moves to flick and hold down a micro switch when you turn on a hot tap, letting the boiler know its time to let rip and go into overdrive and fire the burners up full.
When the rubber perishes (5years+) then the water pressure from the mains can no longer keep the micro switch open so water is no longer super heated.
Test this by disconnecting the leads to the Diverter valve micro switch and check the resistance across the terminals with the hot tap on for a minute or so…you should also see the plunger in the valve move when the hot tap is on.
You can get reconditioned valves on e-bay but its a very tricky job getting all the O rings to seal again.

Mastiles, can't you and the neighbours do the work yourselves? Just all muck in and dig a new trench, new plastic pipe, sorted. You would just need to pay someone to dig the public side and connect it up.

Had a very similar problem caused by the heat exchanger getting a build up of gunk on it cvaused by hard water and crap in the heating system. Had a new exchanger and a system flush and no more problems yet (fingers crossed)

Mastiles, can't you and the neighbours do the work yourselves? Just all muck in and dig a new trench, new plastic pipe, sorted. You would just need to pay someone to dig the public side and connect it up.

Mix of private, rented and empty properties. Hell, we can't even get people to agree to fix the badly potholed road, never mind anything else. If we ever did it, we would pay someone to put in a dedicated pipe (assuming neighbours will let us dig the road outside their properties which technically belongs to them) straight from the main on the road (the water authority will connect that up for free) but at £2/3k it is an expense we can't afford right now.