How do I remove PCB board?

The 407677 pcb in my potterton profile 40 is faulty ( thanks to this site for finding answers to symptoms). I can get a service exchange, but need the old board off intact. It seems to be held in by 4 plastic lugs. I pulled quite hard against these, and tried squeezing them in on the top, but the board resists coming away. I don't want to use excessive force and break it - howz-it-done?

Also, having diagnosed that the board has either faulty electrolytics or dry solder joints and needs servicing, I have also found that I can make the boiler fire by holding the reset button in. Its not clear if this is part of the pcb fault, or a compound fault with the overheat cut-off. The overheat has not clicked out, and if the boiler is down to stand by pilot, it fires only while the button is held under finger pressure, going back to pilot as soon as pressure is removed from the reset switch. Is this symptomatic of a compound problem in that the overheat is faulty. Is there a test? The wiring diagram indicates that the switch is normally on, so bypassing the cut-off by hot wiring the two brown leads on the cut-off should provide a permanent on, and prove the switch as good or faulty. Is this a right hypothesis?