Fuel grease boiler - heat is OK, hot sea extremely puny? I have a hot wet storage tank and videotape circulator pump (TACO...

I have a hot wet storage tank and videotape circulator pump (TACO 006).
The burner and the heating work fine, but the hot dampen is missing.
How to troubleshoot?
Could it be the cartridge or the thermostat?
Staining concrete?
Answers:    Sounds approaching the thermostat that tells the circulating pump when to come on. Open the little panel at the bottom of the reservoir and see if it comes on when you push the contacts together......with something non conductive, obviously.