Biasi 24S Combi Boiler: Wonky Hot Water supply

[keithbrown53]

Hi

4 days ago, we moved into a new (to us, it was built in 1980) house.


It has a Biasi 24S combi boiler, which does the central heating, and
the hot water.

Boiler has 1998 stamped on it.

The house is on 2 levels. The boiler is upstairs, behind a partition in
the bathroom.


Upstairs has a bathroom, and an en-suite.


Downstairs is the kitchen.


The heating is fine, but the hot water is intermittent.


Opening a hot tap in the bathroom or en-suite results in cold water for
10 - 15 seconds.


The boiler fires up. The water then gets warm, sometimes even hot, but
then the boiler turns itself off, and the water runs cold again.
Occasionally, it does stay hot, but more usually goes cold again.


The shower in the bathroom is a mixer, and performs the same way as the
hot taps.


The shower in the en-suite is an electric one, and stays hot: I assume
this is because it heats water as it goes along?


The hot tap in the kitchen, while not fast, seems to keep the water
hot.


The pressure out of the cold taps is huge.


The hot is coming out much more slowly. I'd estimate it would take
20-30 mins to run a bath.


What are the likely problems here? Aside from the intermittent hot water problem, can the flow rate of the hot be increased, or is this just a side effect of having a combi?


The previous owner has the place covered by a service contract with
Scottish Gas, and they are coming on Friday; but fore-warned is
fore-armed, etc.


Cheers,
Keith.

 

[EliteHeat]

The most likely problem is a sludged up secondary heat exchanger causing the boiler to reach temperature and shut down for a short period. The sludge (on the primary water side) prevents a decent flow rate and therefore heat exchange to the mains water.

Either that or you have a duff thermister but my money would be on the HE.

 

[Agile]

Yes its the sludged plate heat exchanger.

But this is not normally covered by the maintenance contracts and might even make a visit by them chargeable.

We charge £136 to clean and service the boiler in London. If the system is very dirty then it could get blocked again and to prevent this a power flush would be necessary at about £300.

The vendor is responsible for selling the house with all the services functioning correctly unless any defects have been admitted. However a boiler engineer's repair is cheaper than even saying "good morning" to a solicitor!

Tony Glazier