Secondary Heat Exchange

[spuddy]

I have a s24 heatline combi. Over the last few weeks my mixer shower and hot water have been flowing hot and cold. If running a bath I only have to run the hot tap as it is constantly running hot and cold!

I have called out BG as I have a homecare agreement. They have advised that it could well be my secondary heat exchange that has scaled up. (I live in a hard water area). TO replace it they have quoted me 105.00 as my homecare agreement doesnt cover scale problems!

As a bit of a red herring, when running the bath last night, i ran the hot tap a lot slower than usual and the hot seemed to come out almost scolding for a while! A hotter bath at last.

Any ideas or do you think 105.00 is reasonable.

The boiler is only 2 years old!

 

[Shaun71]

Ive got a simlar problem.

My boiler is a Vokera Excell 80SP

When running a bath, the temp on the boiler gets to about 60 degrees then cuts the boiler out. Cold water is then pulled through the taps. It then builds back up to temp before doing the same leaving a luke warm bath.

Insurance people came out and changed the thermistor and still the same. They now recommend a power flush to hopefully solve the problem. Quoted £450 + VAT. Got a second quote of a local Corgi registered plumber of £200 + VAT but without no guarantee of working.

I know its a seperate circuit but I have just removed all the homes rads and flushed them all out. I expected the water to be dirty but not at all.

Is there any effective way I can flush the secondary heat exchanger myself?

 

[Agile]

Spud, those cheaper boilers are usually installed by builders and unregistered people without power flushing the system.

That causes rusty debris from the rads to block the heat exchanger. Its not due to lime scale but its not usually covered by insurance.

The secondary HE has to be removed and cleaned. It does not need to be replaced.

We charge £136 for this in the London area and do a little improvement work on the system water but cannot give a guarantee with power flushing.

Tony

 

[ollski]

lime scale will result in a much reduced water flow combined with intermittent hot and cold wheras the sludge will run hot and cold but still at full bore...does it overheat aswell?

I should imagine the 105 repair fee is for the heat exchanger alone with free labour so it's not too bad.

If you powerflush a combi with a plated hx you should replace the hx afterwards anyway as the flaking from the pipework will block it solid very soon afterwards. I sometimes clean the old one like on a glowy cxi but generally I replace them as it is impossible to judge the condition.

If you live in a hard water area it is madness to install a combi without a scale reducer.