Sticking Gas Solenoid Valves?

Your Trumatic gas cab heater hasn’t been used for a while and won’t fire up. You trace the problem to the gas solenoid which operates using electromagnets to open sealed gas valves not opening to let gas flow. How do you free up the sealed gas valves if they’re stuck? If you have some rare earth magnets from an old harddisk, they have enough strength to do it. Don’t mix up the high and low jets as the resulting smoke looks quite scary. At least my brother might not have such a cold weekend now!