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No hot water on mixed outlet

Hello all, I have a boiler in a 50 apartment building that won’t put out any hot water. I’ll lay down all the facts out at once in hopes that one of you guys have an answer for me. I got a call 3 days ago about a faulty 2” Holby Mixing valve as pictured. The mixed side of the valve was ice cold. I figured since I can hear the taco pump running (at least I hope it is) that it’s the mixing valve so switched it out. I put everything back the same way it’s been for the past 60 years, except I added a ball valve to the hot inlet. Basically, the same problem is still happening. At this point I know all the valves are on. There’s no aqua stat, no press gauges anywhere. Should I replace the pump?


    EBEBRATT-Ed Member Posts: 15,710
    Hard to tell without more pictures. I will make some assumptions:

    Hot water from tankless heater flow is into the ball valve on the RH side of the mixing valve.

    Mixed water is vertical riser out of mixing valve

    Cold water goes in left side of mixing valve and feeds cold water for tankless heater.

    Small pipe with gate valve and check valve that goes back into cold water is HW circulation return.

    Why is tee open on mixed water and not connected to hot water to building?

    Draw some hot water and see if the HW out of tankless is hot (boiler temp) mixed water out of mixing valve should be temp the mixing valve is set for (120) Cold water into mixing valve is cold. Return from and of Hot water loop should eventually warm up if pump is running.

    I don't see circ pump. If it is not running, you should get hot water, but it will take a long time.

    Is that an Iron Fireman boiler?

    You could put a valve in the cold water to the mixing valve so you could choke it a bit just for testing.

    The boiler has to be running to get HW out of the tankless. I see this is a steam boiler is the boiler water level ok?