High Efficient Combination Boiler?

It definetly sounds like a faulty divertor valve. However before you noticed this problem was the HW ok. The diverter valve has a tendency to seize up if the secondary heat exchanger has been blocked.
You can only see the data badge for this boiler from viewing the boiler from the underside (by the pipework) it is located on the right hand side panel closest to the back wall.

j
June 2009

This table can be useful

http://www.homeheatingguide.co.uk/efficiency-tables.php

It's a Ravenheat boiler - if it has a built in timer it's probably an RSF 84ET or an RSF 100ET

If it doesn't have a built in timer then probably RSF 84E or RSF 100E

The difference between the 84 and the 100 is the heat output - 84 = 24.1 kW and 100 = 29kW

The efficiency according to the table is about 77% which is quite low. "High Efficiency" is probably just marketing hype. 90% efficiency and more is not uncommon in modern boilers.

I am not a boiler person and put lots of rubbish answers in here but I would guess the diverter valve is playing up - you probably need a service engineer. They are all excellent and none of them ever guess what the problem is - like I do.

http://www.diyfaq.org.uk/plumbing/combi.html

Good luck...

Peccavi
June 2009