The pressure guage on the front panel reads the pressure of the water that circulates round the boiler and the radiators. It should read around 1 bar (15psig).
The most obvious reason there is no pressure is that water has leaked out of the system.
You can top it up again via the filling loop. The incoming cold water main goes to two taps, one for the water to your hot taps, one for topping up the system.
Add water till you get to 1bar (the middle of the green range of pressures on the guage) and then close the tap.
Turn the central heating on, and let the system warm up while you watch the pressure guage. If the pressure goes right up to 3 bar or so, and then hot water comes out of an overflow (hopefully outside) then your expansion vessel needs refilling or replacing. When the pressure goes up a lot on using CH it is a very good time to get the thing serviced.
Get a recommended local Vokera trained corgi man to do it, phone Vokera for a name.
If the pressure doesnt rise much when CH is on then you may have a leak somewhere, you can get Fernox leak sealing concentrate to inject via a radiator bleed point using a mastic/caulking gun.
Running a boiler with no pressure can be (very) damaging. Most (all?) modern ones have an under pressure lock out to stop this happening. The Vokera 80sp does not. If you run it this way (low/no pressure) and the boiler flow switch is sticking in the 'OK' position (as it may if it hasnt been regularly serviced) it could fire up with no circulating water and self destruct.
If you have no manual, you can download a copy from the Vokera website. Or you could phone Vokera for advice 9-5 mon-fri.
New boilers are expensive, and can be very expensive to fit. And they need servicing even more often...
Newsgroup uk.diy has advice on refilling the expansion vessel in the combi FAQ.
cd, March 2007
