Ash wrote:
No, the type you describe was always relatively uncommon and AFAIK
no-one makes that type any more (i.e. as high-efficiency/condensing
boilers). Much more common is the arrangement whereby the primary
gas-water heat exchanger heats water that goes either to the
central heating or to a secondary heat exchanger that heats the hot
water. These secondary heat exchangers are usually plate types
(PHEs) and these are susceptible to scaling ('furring') up on the
secondary, domestic hot water, side, or to getting blocked up with
gritty magnetic debris on the primary side from the water that also
goes round the radiators. In my limited experience of this
phenomenon it seems to be Baxi Combi 80 or 100s and Potterton
Performas (same model, different badge) which are susceptible.

Checked again with my mother and it's a Ideal Boiler HE30 and yes your
correct it's got a Plate Heat Exchanger .. (accordingly to the manual
she has).

If she doesn't have one fitted then, whilst they'll
fix the heat exchanger with a sonic cleanse this time,

Interested to know what a 'sonic cleanse' is.

We're not sure what a sonic cleanse is also ... perhaps some sort of
ray gun 8-( ?

Looks like we'll be waiting a while ... they've booked her in for 14th
November to come and do the repairs. She's in her 70's and they
consider it reasonable to let her wait over two weeks before she can
have a bath. I think a nice strong phone call is in order first thing
in the morning.

As good as ever a reason for not having a combi boiler. With a DHW cylinder
and an immersion heater she would still have had hot water at least.