Indirect water heater question

Hello,
I have a Crown oil boiler and Crown megastor 40 gallon indirect water heater. The system has 3 zone valves but a single circulator (water heater is on zone 2).
Today we had only lukewarm water coming from the faucets. The zone valve for this zone is open, the boiler is working and there is pipe from the boiler to the water heater is hot. But the pipe coming from the water heater returning to the boiler does not get hot.
The other two zones are getting heat so the circulator seems to be working properly.
This problem has happened several times in the past few weeks and it seems to start working again for a while.
Has anyone had this type of problem? I appreciate any advice that you can offer to me.
Thank you in advance,
Scott
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The zone valves are Honeywell model YHV8043E1012. Thank you for your reply and advice.
Scott
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OK, sounds like typical Honeywell valve with two yellow wires and two red wires. The red wires are the ones for the end switch. Typical zone valve wiring is a birds nest mess, so be careful not to pull apart any splices while you examine it. What you will find is that the red wires from all the zone valves go together and are spliced to one pair of wires that go to a relay box, probably on the face of the boiler, above the burner, and are attached to the "T T " terminals in the upper left hand corner of the box. Trace out the two red wires from the offending zone valve, and be sure they are securely spliced to the others. Turn up the aquastat on the indirect, it's zone valve should open, then the circulator should kick on. If the zone valve opens, but the circulator doesn't kick on, strip back a little insulation on that valves two red wires and touch the two wires together. This is 24 volts , so no need to worry about getting fried. If, when you touch the two reds together, the circulator comes on, you have a problem in the valve, with it's end switch. The entire head of the valve is replaceable, or you can possibly just get a new switch. Personally, I'd get the entire head.
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I checked the red wires and they were pretty secure with wirenuts. I turned up the temperature on the front of the aquastat on the water heater. The boiler kicked on and the zone valve opened for this zone. Once the boiler turned off, I could hear water moving through the circulator. The pipe below the zone valve was hot, above the zone valve was also hot. A the water heater the pipe in from the boiler was hot, but the pipe coming out of the water heater does not get hot. None of the pipes on the return side get hot.
I also turned up the thermostat in one of the heat zones upstairs and its zone valve opened too. So both its zone valve and the water heater zone valve were now open. The circulator was still going and within a minute or two, the pipes on the return side of the heat zone was hot, but the return pipes for the water heater were still cool.
Do you think it could be air in the pipes inside the water heater? Or is there someting else that could be wrong with the water heater or another part of the system?
Thanks again for your advice.
Scott
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With the heating zone turning on and confirming that the circulator is functioning, it narrows it down to two possibilities, an obstruction in the indirect's hot water loop, or air. I would have the system purged, which will either eliminate the air or show up the obstruction, which can be solder logged in the zone valve or a broken valve

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Hi,
I wanted to close the loop on this post. I tried to purge the system and checked for physical obstructions in the water heater coil, but still had the problem. I was stumped so I had a plumber over and the problem turned out to be the aquastat on the boiler.
The aquastat was firing the boiler but wasn't turning on the circulator pump.
I had ruled out the circulator pump because it's shared between 3 zones and the other 2 zones were working.
The plumber told me that those zones could have been getting heat by gravity because those zones are on the ground floor, one floor above the boiler. The water heater is in the basement with the boiler so the water heated by the boiler was getting to the water heater inlet, but didn't have enough momentum to circulate through again.
I had no idea that this was even possible, but after the aquastat was changed, the water started to circulate normally and both the inlet and outlet pipes on the water heater got hot immediately and we had hot water in a half hour.
Gravity feed to the 2 heating zones upstairs isn't something I would have ever considered as a possiblity. It's been so cold here the last few weeks -- in the teens at night and 20s during the day -- and heat upstairs has been working fine. All while the circulator pump was off!
So I'm writing back to give a resolution for this post so others will benefit from my experience as I have from so many posts in this group. And thank you RBM for your advice. I'm sure that had you been here or I'd given you more detail during our thread, you'd have come to this conclusion. I certainly learned a lot more about the whole heating system.
Thank you!
Scott
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