Worcester greenstar 28i junior keeps losing pressure- doesnt stay at 1.5 bar when off

[PHIL269]

I have repressurise my Worcester Greenstar 28i junior boiler but after central heating or hot water is run it goes back to zero bar when not on.
When heating is on it stays near zero bar and when heating is on the pressure goes up to 2 bar

The heating and central heating are working ok, but just wondered if this is normal as I thought it should be at 1.5 bar when boiler is off ?

I have never bleed the radiators would this cause the problem and I haven't serviced the boiler for a while could this help ?
Any advise is much appreciated please.
Thanks
Phil

 

[picasso]

Pipe leaking outside ? and yes a service would help.

 

[PHIL269]

Thanks for the reply.
Who is best to service it , british gas or Worcester or should I try local.