I have noticed that when the heating (thermostat) is turned up to 25 the pressure gauge just above the expension tank goes up from between 1.0-1.5 psi to over 2 and sometimes 3 !!
At one point, when the pressure was high just over 3psi, water overflowed out of the expansion tank. When the thermostat is set at around 22 the pressure goes down and remains at around 1psi and sometimes slightly lower.
My questions are:
Should the pressure remain constant between 1.0-1.5psi regardless of whether the heating is turned up or down?
Does the expansion tank need replacing or topping up? I heard in some cases they need air pumped into them?
Finally, if it is the expansion tank, then how much are they?
Thank you :)