Amtrol water heater WH-7P gets barely warm water

I had the same problem. I had a steam boiler and the water level in the glass gauge was below the top of the coil of the tank. remember water finds its own level, so it settled at the glass gauge level, therefore air got in coil.

to resolve problem : turned on manual water feed to boiler to raise water level. as water level got higher, let out water in hosecock between boiler and amtrol. amtrol noticed hot water reduction, circulator clicked on, boiler kicked on, turned off hosecock, turned off manual feed. I effectively bleed water out of line by running water out of amtrol as water feed in boiler increased water level above coil.

took a while to figure this out, so if this is the problem, dont feel to bad. keep water level of steam boiler high.

From what you are saying it sounds like an issue with either a circulator pump or a zone valve. It depends on what type of system you have ... if you have a circulator pump that only runs the Amtrol then that is probably bad. If you have a zone valve system then it is probably the zone valve if you still have heat for the rest of the house. If you have no space heating then it is probably the circulator pump.