Honeywell L8148E Low Voltage Problem

d_a_parker

Hello,

I have a boiler with 3 zones and a Honeywell L8148E 1216 aquastat. I've recently started having a problem with my heat, and I think I've traved the problem to this aquastat.

The system works fine most of the time.
Thermostat calls for heat, aquastat gets 24V between B1 and B2, damper opens, and the burner fires up. But a few times each day, the burner doesn't fire despite a continuous call for heat, sometimes for hours. When this happens, the aquastat has only 12V between B1 and B2, so the damper never opens and the burner never fires. If I close the relay in the aquastat manually, the cycle finishes and everything keeps working for many hours.

I have seen other posts about no voltage on those terminals, but I can't find anything about this half-voltage issue I seem to have. I'm wondering if anyone knows what might cause that to happen randomly, and/or whether or jot replacing a part in the aquastat could fix it. Or, should I just replace the aquastat itself?

Thanks!

STEVEusaPA

First I would shut off power and check all wiring connections, see if that helps.
Check to make sure you are getting clean 120v into the control.
If you remove the thermostat wires (or end switch wires) on the control-should be T & TV, jump them out, and are not getting a consistent 24v at B1 B2, replace the control.
If you are getting consistent 24v, you'll have to start checking all your wiring. As systems heat up, low voltage wiring is susceptible to damage, which could be why you see an intermittent problem.

d_a_parker

Thanks for the suggestions, I will give that a try. I checked most of the wiring already and it looks sound, but I didn't try jumping T and TV. Unfortunately, I could jump those terminals any number of times and get the correct 24V, but that could just mean I got lucky during my tests. It's been a frustrating experience because this is one of those problems that is so intermittent, it's pretty much impossible to reproduce on demand.

Thanks!

Tim McElwain

There has been problems with the plug into the relay from the vent damper not making good contact on this model L8148E relay. Sometimes if you wiggle it then it works for a while. I would have professional take a look at it and determine if it is the relay plug in or the plug itself. You may need a new relay.

SuperTech

> @Tim McElwain said:
> There has been problems with the plug into the relay from the vent damper not making good contact on this model L8148E relay. Sometimes if you wiggle it then it works for a while. I would have professional take a look at it and determine if it is the relay plug in or the plug itself. You may need a new relay.

This is absolutely correct! I've seen this problem a few times. If I were a gambling man I'd bet the house that that's the problem.

HVACNUT

> @d_a_parker said:
> Hello,
>
> I have a boiler with 3 zones and a Honeywell L8148E 1216 aquastat. I've recently started having a problem with my heat, and I think I've traved the problem to this aquastat.
>
> The system works fine most of the time.
> Thermostat calls for heat, aquastat gets 24V between B1 and B2, damper opens, and the burner fires up.

That's not the correct sequence. A call for heat will go through the limit then to the damper motor. Once the damper opens, an end switch is made and sends power to B1. So if the damper doesn't even open sometimes do as @Tim McElwain said and make sure the molex plug is fully seated in the aquastat and the damper motor.
If the damper opens but no 24v to B1,B2 then theres a little black switch on the damper motor at the end of the plastic cover. You can switch it to manual open and the damper will remain open. If the problem goes away it's a bad end switch in the damper motor. The damper itself is for efficiency.
If all connections are good and the problem remains its probably an internally bad 1K2 contact in the aquastat.
If it is the aquastat that's faulty, there are more choices than a direct replacement. The Hydrostat can support low water cut off and efficiency settings.

d_a_parker

Hello,

Thank you for all the the suggestions. I don't see a molex connector in the aqustat at all, though. The only molex I see is outside of the aquastat, and joins 8 wires (four 2-wire cords). 2 of those wires come from the aquastat: 1 from B2, and the yellow wire from the damper.

> @HVACNUT said:
> That's not the correct sequence. A call for heat will go through the limit then to the damper motor. Once the damper opens, an end switch is made and sends power to B1. So if the damper doesn't even open sometimes do as @Tim McElwain said and make sure the molex plug is fully seated in the aquastat and the damper motor.

Thanks, but I just put a meter on the aquastat again and watched when until the boiler temp fell enough to trigger it. B1/B2 went from zero to 24V just before the damper starting to turn (a 1 sec. difference maybe) and then the burner lit up once the damper was fully opened.

When the boiler fails to light, B1/B2 only get 12V and then nothing else happens. No damper, no gas valve, no burner. It just stays at 12V until I force the relay, then it works correctly.

I ordered a replacement aquastat and hope to install it in the next few days. Unfortunately, I don't have time to troubleshoot this much more because we're experiencing quite a cold snap in our area, and the house keeps getting cold while we're at work and no one is here to make sure the heat keeps working. Perhaps I'll test this aquastat further when it's off the boiler and on my bench.

HVACNUT

Where does the wire from B1 go before it gets to the gas valve? An ignition module? It should be going through the spill switch, rollout, and any other safeties in series to the gas valve.
If B1 powers an ignition module then the problem might not be the aquastat. That might also explain the 12v.
A pic of the wiring diagram would help.

d_a_parker

Hello,

B1 is the orange wire from the damper. B2 goes to the gas valve. A photo of the diagram on the boiler is attached.



Thanks!

d_a_parker

I decided to ride this out for the last few days without replacing the old aquastat. After turning the speed down from medium to low on all 3 pumps, I have let it go for about 4 days without a single low voltage issue. The pumps were set to medium speed for several years prior to this without any issues, and I have not tried turning the pump speed back up to see if the problem comes back. But does anyone know why that would matter? It's also possible I'm just having a streak of good luck, since the problem was so intermittent to begin with.

Thanks.

Jamie Hall

Bad connection or contact somewhere in the sequence.

SuperTech

I highly doubt that the pump speed has anything to do with this problem. I think you might have been lucky that the problem hasn't occured again. I would just replace the aquastat, it only takes 10-15 minutes.