Somewhere on the boiler or system is a red expansion tank, have a look from on top of the boiler, they're usually at the back. Once you have found the expansion tank, locate the valve on the tank, its the same as the valve on your car tyres. Once you have found the valve, give the pin in the valve a quick press, if water comes out of it, you need a need expansion tank, if its just air then you need to re-pressurise the tank. You can do thing in two ways.
Way 1(the correct method)
if you have a drain tap on one of your rads (it looks like a ribbed tail) shove the garden hose on the drain point and open the tap, this is letting the (water) pressure out of your system, (its just the pressure/your not draining the hole system) so check the pressure gauge on the boiler, your looking for 0mb. Once the system is at 0mb, close the drain point off, take the car foot pump and pump the expansion tank to about 1mb. Open your filling loop and top the (water) pressure up in your boiler to 1 or 1.25mb. Your done.
Way 2.
This way will work but may take a be of trail and error. forget all about the drain point and dropping system pressure, and just use the foot pump to put a little pressure into athe expansion tank a little at a time (ignore the foot pump pressure gauge reading) So maybe do 2 or 3 pumps of the foot pump, put your heating on for 20 minutes and see what the (water pressure rises to) your looking for anything around the 2mb or 2,5mb mark, if it goes back to 3mb, put a bit more air in the expansion tank(2 or 3 pumps) and see what the boiler pressure gauge is reading after the 20 minutes or so, keep on repeating this until you get to 2mb or 2.5mb with the heat on. Job done.
As for it being dangerous, it the pressure getting high the blow off(PRV) will just let a little hot water out and should shut off again. hope this helps
LTGF, August 2008
