Welcome! Here are the website rules, as well as some tips for using this forum.
Need to contact us? Visit https://heatinghelp.com/contact-us/.
Click here to Find a Contractor in your area.

Heatmaker Mark 2 - not enough domestic hot water

Steve M_2
Steve M_2 Member Posts: 121
Flushing the coil is a fairly easy thing to do. Just isolate the coil with ball valves and install a boiler drain on the inlet and outlet. Then pump Sizzle, which is probably safer than muratic acid we used to use, throught it and in both directions for 20 minutes. If you do use muratic acid, make sure to neutralize it with baking soda.

Before doing that, make sure the mixing valve is working properly and the Low limit switch is functioning correctly. I assume when they updated the vent they cleaned the exterior of the heat exchanger coil?


  • Chris H._2
    Chris H._2 Member Posts: 11
    Heatmaker Mark 2 - not enough domestic hot water

    Hi! - I have a vintage 1992 Heatmaker Mark 2 boiler with domestic hot water coil. The unit has the newer board and updated vertical vent. The boiler section for the baseboard heat works fine. The problem is the continuous supply of domestic hot water. It comes out of the spout hot but turns to lukewarm after the 2nd gallon when filling a 5 gallon bucket. My heating pro who has helped me keep this vintage unit operational says the coil is the problem with poor heat exchange. He is recommending replacing the entire boiler with a similar unit. Is there any way to service the coil to improve its heat exchange i.e. flushing the tank and coil to remove sediments and scale? I am not ready to ditch this unit if a good cleaning can bring back the the domestic hot water. thanks for reading and any comments - Merl in Massachusetts
  • kpc_75
    kpc_75 Member Posts: 37
    back flush the coil

    pretty common to see coil lime up. Sizzle works well. You do run the risk of causing a pinehole but if it has not been done before 1 time should by you some time.
This discussion has been closed.