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I have a RayPak 136-T HW Domestic Heating Boiler that has the modulating gas valve Honeywell trade name "modusnap valves". This valve isn't working, it doesn't respond properly causing erratic water temps. And will soon fail making the heating totally inoperative. I've tried to get a new one but it seems that they are not available and those that do have one are asking rediculous prices. can something be substituted for same or can this valve be rebuilt as the thermo bulb may be the problem and lost some of its hydraulic liquid causing the valve to act erratic.