Sabre 24 combi boiler - fluctuating hot water temperature

[AxelO]

Hi,

Having major issues with a Sabre 24 combi boiler and fluctuating hot water temperatures!

As background, problem started when hot water temp began fluctuating when the CH was on. Not the end of the world but annoying so got an engineer round who said new heat exchanger was needed. He also left me with the gift of fluctuating water temp whether CH was on or not by the time he left - nice!

More serious problem now so decided to get the heat exchanger replaced - this fixed the problem for 4 hours. Got the engineer back who then replaced all the thermistors which fixed it for another 4 hours before same problem again. The wife was getting less and less impressed by this stage!!

Got another engineer round to have a look (original guy was on holiday!) who said heat exchanger needed to be replaced again and the system flushed (which wasn’t done 1st time). He explained the boiler is firing up, then shutting down continuously as it can’t send the hot water out quickly enough. This seemed to make sense as when watching the pilot light when the hot water was running - the boiler made a kettling sound before shutting down and then firing back up again every 30 seconds or so and kept following the same cycle.

Bit reluctant to replace heat exchanger again and flush due to the high cost and general indecision around what the problem actually is – any advice please!?

And not sure if its just a wild coincidence, but round about the same time the problem started, two doors down began work on an extension which is still ongoing – someone mentioned this might be causing a fluctuation in pressure which might be causing the problems – any truth in this?

Thanks in advance…

 

[spacethegas]

it sounds like it wasn't flushed & chemically treated properly when the boiler was originally installed.

this is very common when a cheap boiler is cheaply installed. i'm not necessarily putting yours in this bracket, but it sounds an ideal candidate.

 

[tonybhoy]

You would have been cheaper replacing the boiler at £349 however Vokera do a fixed price repair for £145+Vat.

Has anyone checked the working pressure at the gas meter and boiler?

Could well be the Venturi that is the problem. Vokera recommend they are replaced.

Someone will be along with the part number shortly I suspect

Vokera: 08703330220

They are open from 8.15AM tomorrow.

 

[AxelO]

Given Vokera a call but they don't cover my area (Eltham, London) so just gave me the number of their approved local agent who don't offer the same fixed price deal

Am sure it was a cheap install as it was there when we moved in two years ago and we're beginning to find everything was bodged!

Pressure gauge on boiler reads 1bar and not moving - not sure about gas meter...

Any link to the building work down the road you think?

 

[spacethegas]

doubtful.

 

[tonybhoy]

Doubt it but you never know which is why I asked if the WP at the meter/boiler had been checked.

There's a Vokera service engineer on here who'll no doubt put you in the right direction but I think it is gas pressure/ fan/flue/venturi related.

BG do a fixed price repair for £99 if you are a BG gas customer or £168 depending on your postcode or homecare for about £36 p/month foir the first year.

 

[Sloop]

looks, exactly like the vokera compact 24 inside, same H/E 10021419. mains pressure big problem with these anything over 6bar reduces life expectancy. Like tony says gas/press need checking.

 

[tonybhoy]

looks, exactly like the vokera compact 24 inside, same H/E 10021419. mains pressure big problem with these anything over 6bar reduces life expectancy. Like tony says gas/press need checking.

 

[Paul Barker]

I wasn't aware of the venturi failure issue on these but typical vokera to get venturi problems

my money was on plate heat exchanger but I would have hung around long enough to ascertain it properly and would have detected venturi related failure as an alternative diagnosis.

It really takes a little patience to properly fix a boiler and so many of the guys seem to be bish bosh bash that's what yer want mate merchants.

It's like the customer's who stand there forsing a decision from you before you have listened to the boiler (which you can't do because they are yapping a load of drivel which even einstein couldn't make sense of, listening to many customers explain what has been happening, is like listening to a toddler explaining how to do a heart transplant, and likewise explaining to a customer what is happening in their boiler is like training a toddler in 30 seconds to perform a heart transplant) When will people realise if they want know what is happening in their boiler they need to spend the time (about 5 years) in the discipline befoire we can even have an intelligent conversation one with another about it. So stop leaning over us and foot tapping turn off the telly prevent the dog establishing what sex we are shut the crying infant in it's room and go back to loose women.

 

[Sloop]

Maybe venturi on the HE model, can't see it being that on this boiler, and there is no plate HE. The main HE is known as a bithermic HE split into two parts with h/w running in one half heating in the other.

 

[heatingman]

gas pressures, working/modulation

 

[Sloop]

When they fitted new HE, did they clean the two flexible pipes L/H side of boiler? these can get blocked with crap from system and cause it to kettle or overheat.

 

[AxelO]

All helpful stuff - thanks for the replies guys.

Is the gas/water pressure something I could possibly check myself or do I need to get the professionals in?

Unfortunately wasn’t there when heat exchanger was replaced so not sure what was done but apparently the guy was in and out like a shot so don’t think he done an overly thorough job!

Not sure if it helps diagnosis, but have noticed that the problem tends to go away when the kitchen tap and occasionally bath (via a mixer tap) are used at full pressure (i.e. taps are turned all the way on). It never works with the bathroom sink tap though where pressure has never been high.

Thanks again for all the input to date…