No heat in one hydronic zone

veeder1

I have been in the field for over 40 years and came across this problem that I wonder if anyone else has ever witnessed and if so what was the cure. I have a 6 zone hydronic system that has taco circulators that have the switching relay incorporated within. The system has been installed for years and was working fine. I was called and discovered that one zone was not working. After checking the circulator was pulling high amps so I changed the circulator. The system did not change and the zone did not change. Here is the tricky part. When the zone is calling by itself it works fine. When there is a call on all the other zones we loose flow through the one zone that I changed the circulator on. The boiler pressure is at 15psi and it is a single story ranch. The zone that is having the issue is piped using radiators and the other 5 zones are baseboard. As I said nothing changed in the piping. Customer just said no heat in that zone. Anyone got any ideas??

Big Ed_4

I would think it lost the pressure drop when the other zones are running . I know you mentioned it has been working fine for years . Curious how it was piped and location of expansion tank ..

veeder1

The expansion tank is on the supply and the boiler is on the first level. The supply pipe runs approx 15 feet down through the floor and goes into the 6 circuit header. The loop in question is in the middle and only has 4 short sections of baseboard on it. Some of the other zones have radiant and are much longer. When that short run operates alone it is fine. As the other zones kick in the flow will decrease in only the one zone. I detect this by monitoring the return temp and it drops. All the other zones work fine. The returns all come back to a common return header. One other thing is that there is a heat exchanger in the return for an outside wood stove. Just wondering if that could be creating enough of a pressure drop to affect the system. The thing that is puzzling is that this system was working fine for years. Any thoughts?

Jamie Hall

If it's been working fine for years and rather abruptly isn't working... something changed. The question, of course, is what -- and it may not be at all obvious.

When you say the zone doesn't work, what exactly does that mean? No flow through it, or very little? If only one or two of the other zones are running, rather than all of them, what happens to the problem child? Do you have -- or could install -- any way of seeing what happens to the supply and return pressures (not flows, not temperatures) as various zones are running?

That heat exchanger shouldn't make any difference, if it's common to all the zones.

Big Ed_4

I like a clean slate when approaching a job . It does not make sence when the home owner goes on telling me what the last tech thinks the problem is when they did not fix the problem , Just saying not thinking of you . As Jamie asked what has changed . When was the wood stove heater added . . Is there another tank on the wood stove ? Two tanks two locations , the system gets sloppy . Just thinking

The location of the expansion tank matters from the circulators. . .... Several zones pump away from expansion tank and the problem zone is pumping toward a expansion tank .The zone would loose it's pressure drop and "No Flow " Away from tank increase pressure in loop . Pumping toward the tank pressure in the loop would drop . Two tanks on two locations the circulator will pump from one tank to another .

Being just a grunt. , I need to see and feel ...

neilc

were other circ(s) replaced?
and they're bigger stronger flow?

veeder1

Thanks for all the brainstorming!! This is too much for my one brain cell I have left. The zone in question will work as long as that is the only zone calling. When others call we loose the return temp in the zone in question which is definitely loosing flow. All the other circulators are the same except for one grundfos which was operating fine before. I wish I had pressures in the system because that would tell what is going on. I suppose I could add them but this system was installed by a homeowner (not knocking the homeowners but a homeowner and a youtube video can be dangerous!!) It is extremely sloppy. Our technician was called because of no heat in that zone. He tested the circulator and amped it out. It amped high so he replaced it. That was the only circulator replaced in the system and it was replaced with an exact match. Thought it was fine as that zone worked but soon discovered that when the other zones called we lost flow through the original zone that we got a call from. I will try to upload a sketch of the system later for you guys to ponder. To answer Big Ed's question all circulators are pumping away from the expansion tank.

veeder1

So here is what was found and how it was found. So after checking I confirmed all the piping, position of the expansion tank, etc. I previously said that the system worked for 6+ years and something changed. My tech thought that the circulator was bad because the amps were very high. After replacing the same issue was there with the system. When that zone called alone it worked but as additional zones called the return temperature would substantially drop to the point of very little flow. When he went to put in the boiler drains so that we could get some pressures in the system to find out where we were loosing it he found that the seal in the circulator flange had become dislodged and partially restricted the port. I attached a picture so that you can see what I mean. After replacing the circulator flange and purging the system the real test came. All circulators were turned on and presto. The zone in question started to gain return temperature to the point where it should be. Who would have thought that something this insignificant could cause such a headache!! Thanks for all your help and hopefully this may help you help someone else in the future. I sure know that I learn by experience!! Thanks again for the help and pointing me in the right direction!!!