Boiler fires but no hot water the taps

[ekd4176]

My domestic hot water stopped mid shower today. The boiler is firing and the pipe leading to the indirect water heater is hot on both sides of the Taco circulator pump. The boiler seems to be running a little hot and the baseboard hot water system is working and puts off heat. Any thoughts?

 

[Dana]

The shower mixer's anti scald valve might be broken. Is there hot water at other taps?

If the Taco is fried it could be heating the adjacent pipes that it's hooked up to even with minimal or no flow. If there is boiler-flow through to the indirect both the supply and return pipes between the boiler & indirect should be hot.

 

[Sponsor]

 

[ekd4176]

Sorry for the delay and thanks for the response. The supply to the indirect was hot but the return was not. I had no hot water at any taps in the house. After cranking up the heating loops I got hot water to the taps and everything went back to normal. (That is the only thing I did that seem to "fix it"). I did notice however that every tap I tried gurgled at first and let off some air but then all was good. Any thoughts of something I should be looking at? I have seen some mention of being "airbound" on some other threads but I have no clue what happened.

 

[Jadnashua]

Air in the boiler lines can prevent (lock) the flow. So, yes, purging the air can make it all work right again. But, what might be worth trying to investigate is where the air is coming from. Air implies a leak, which requires make up water, which, long-term addition of potable water into a boiler system leads to more rapid degradation of the components. Potable water contains some dissolved oxygen, and that's what causes things to corrode from the inside out. WHen it's sealed well, after the initial fill's air is locked up (in rust, for the most part), with no more being introduced, it's pretty much inert.

 

[Dana]

You have no flow, or very low flow. It could be a damaged pump impeller, damaged pump motor (does it vibrate as if it's running?), or a vapor lock from a large slug of air in the loop.

A vapor lock in the heat exchanger inside the tank can stop flow, and if the system has been drained or opened up isn't rare with indirects where both the supply & return ports at the bottom of the indirect. To purge that air requires forcing flow though the heat exchanger by opening up a drain port downstream of the return on that loop (hopefully there is one on your system, while maintaining system pressure with an auto-fill (or manual) valve.

Air coming out of the potable taps would not be a symptom of a vapor lock in the heat exchanger.

It's a bit unusual for a vapor lock to form UNLESS the system has been opened up, introducing a lot of air into the heating system. The prime suspect is still the pump, but go ahead and purge the heat exchanger on the indirect.

A few pictures of the indirect, the pump, and the loop plumbing between the boiler & indirect might be useful here.