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.

Altac Combi

Yadkin Member Posts: 2
I installed this boiler three months ago, and had it working perfectly to heat an indirect water heater. Then I added a second zone using the domestic hot water side of the boiler (a heated towel bar). Again, the system worked perfectly.

For simplicity I'll refer to the boiler side (180F) and the DHW side (120F).

Then I added a third zone, a fan coil to heat the house on the boiler side. Now I can't get the boiler side to work. The DHW side works as before. There is no call for heat from either the indirect or the fan coil. All three pumps are pumping. There is no vapor lock in either loop.

I have tried just about everything. Figuring I got dirt in the three way valve, I flushed both loops backwards and forwards. The valve cycles during the two-minute start up sequence.

I'm using a Taco SR506-EXP-4 Switching Relay for control. All three zones signal "on".

There are no error messages shown on the boiler control panel. No blown fuses.

Any help would be appreciated before I start throwing parts at this.


  • Jamie Hall
    Jamie Hall Member Posts: 23,668
    I'm not familiar with that boiler -- but you mention a three way valve. Can, it, in fact run both heating and domestic at once? Or just one or the othe?
    Br. Jamie, osb
    Building superintendent/caretaker, 7200 sq. ft. historic house museum with dependencies in New England
  • Yadkin
    Yadkin Member Posts: 2
    The valve cycles between CH (central heat) and DHW. Either or.

    The issue turned out to be a blown fuse. However, now I don't get the DHW cycle, the three way valve is now "stuck" at the CH position.