Sounds like the EV, our most common fault.
If you have access to the expansion vessel valve (looks like a car tyre valve) it should be around 21psi when measured.
Also check the pressure relief pipe if its letting water by it'll also need replacing.
Alpina D5 bought 2015
Alpina D3 sold 2015
Last edited by Jedimindtrix; 12-23-2012 at 08:10 AM.