Circulator Pump Stops Running During Call for Heat

MarkW66

I have a 13-year old Dettson Hydra24 with 3 zones that is doing something odd. In my case, the pump (Grundfos UPS, set to medium speed, which I just took apart to free up a seized impeller) runs from a cold start reset for about 5 minutes, then begins to short-cycle on and off until it eventually just shuts off along with the rest of the diodes. The cycling seems to be random as it progresses -- about 3 seconds at first, then randomly 1 second, half a second, then so short the pump doesn't even have time to energize. There is a click from somewhere on the panel every time it cycles on and off.

The heat cycle seems to start normally from a cold boiler. With a call for heat, the diodes light up in this order:
Pump 1, followed about 7 seconds later by
Heat_En & Heat 1, simultaneously
Heat 2, about a second later
Heat 3, 45 seconds after Heat 2

After a couple of minutes, I can feel the zone pipe getting warm. Then about 5 minutes into the cycle, all the diodes will suddenly shut off and the pump will stop. About 3 seconds later, all 5 diodes come back on again as the cycle repeats as described above (Pump > Heat En & Heat1 > Heat2 > Heat3) except it will only run for a few seconds before the diodes go out again. Another couple of seconds later, the Pump diode will come on and the pump will run for about 5 seconds, then the short cycling starts. After numerous on-off cycles, the pump will stop entirely and the diode will not light. A few seconds later, the Pump, Heat En, Heat1, Heat2 and Heat4 (NOT Heat3) will light up, but the pump still isn't running.

Is the Heat 4 diode lighting up an error code of some sort?

Some background:
- I took the pump apart as it would not spin; I was able to free the impeller and reassemble the pump with no problems... or leaks.
- I assumed the seized pump was due to sediment in the water line, so I flushed both the boiler and the 3 zone circuits (individually) and purged them to the best of my ability.
- There are two automatic air vents in the system: one on the Hydra boiler and one at the high point in the zone valve piping -- both have black plastic caps which are slightly open.
- When the pump is running, the flow is slightly noisy around the pump area, but I'm hoping whatever air is in there will work itself out over the first few days of proper running.
- The boiler continues to heat up (and stop) properly after the pump stops running.
- The system is hooked to an Aube timer, but to perform the tests I ran it in Manual-On mode.

Once the system comes up to temperature, I cannot reset the system to get the pump to run -- it seems it only runs when the water is cold/cool, so I have to let the system drop below 70 degrees (the lower limit on the temp gauge) before the pump will run again. This might be coincidence... I don't know. I can repeat this when the boiler is cold but not when its hot.

Sorry for the long post, but any help would be appreciated. When I get another chance, I will capture some video and post it in a follow-up.

Jamie Hall

My bet is on the controller, not the pump. But I don't know much about that boiler's controller.

MarkW66

No, I don't believe it is the pump. When I did the second test, the boiler temp was just about 80 degrees F. The pump ran long enough to circulate the cold water through the system (bottoming out on the 70 degree pin), then start to heat it back up to about 72 degrees F before it stopped running, so that's why I don't think its a temperature thing, either -- at least not WATER temp, anyway. Maybe something else is getting hot..? I'm really hoping its something simple and NOT the board...

I forgot to mention the pressure is ~20psi steady.

I'm going to do another cold test tonight and film it so I can maybe post a short clip.

hot_rod

Float style air vents, by themself, may not eliminate the air properly. And you may be plagued by more air locks until you get a good zone by zone purge.
Or add an air separator at the boiler.

Dave Carpentier

If you could monitor the voltage to the circulator, it would indicate to you if/not the circulator as a problem. When you suspect the circ should be running, but it's not, then voltmeter the terminal connections on the controller ? Obviously, beware the hazardous voltage.

I dont use a controller, but I have had to deal with misbehaving zone valve end switches. As the internal end switches went bad, they would chatter and act intermittent. This would cause my circ (via a relay) to stop and start a lot.

MarkW66

Dave Carpentier said:

...
I dont use a controller, but I have had to deal with misbehaving zone valve end switches. As the internal end switches went bad, they would chatter and act intermittent. This would cause my circ (via a relay) to stop and start a lot.

To be fair, I only tried this with one zone operating -- I'll try one of the other zones to see if the same thing happens. But would that cause the whole set of diodes to go out, or just the pump circuit?