Also check in with Roger Berke, he has a good forum, and is very helpful. If you find you need parts, he is good source - as he always tries to recommend the best components available to be used for replacement.
RV Hydronic Heater Repair - Home
Be sure you have your full model number, can find that down by the unit, or probably on the mirror components listings.
Best of luck on your problem, and please close the loop back and tell us what you find to be the problem - that helps others in the future too.