Can I switch on my valiant combi after 6 months off?

For starters NO you wont blow yourself up as many, if not all, boilers have a safety device in the gas system.

IF YOU are the new owner and intend living in it then for your own safety get it serviced.
If you intend renting the property in full, in part or letting rooms, you MUST by law have a certificate for all gas appliances and this is yearly.

If it's not owned but rented by you then they agent for the owner is responsible to see the certificates are in date and all gas fittings etc are tested annually.
To find a Corgi registerd fitter go to
www.corgi-gas-safety.com
Then select find an Installer near you.
Then follow on screen instructions.
P.s Landlords must show these certificates on request so ask to see then if you are the tenant and make sure the dates on them don't look altered.[there still are 'Cowboys' around.

Bob
October 2005