Glad to have helped Loo. Just goes to show how useful the forum can be.

Seems so many people are having this problem atm that the manufacturers are supplying advice on the website. Anyone who needs it can find it here

http://www.worcester-bosch.co.uk/homeowner/customer-service/common-winter-boiler-enquiries

Our boiler started to sound like a boiling kettle and then went out.

Bluebella I would ask your installer about this problem and how he gets round it.