LWCO voltage to automatic water feeder

petec88

I have a PS802 McDonnell Miller LWCO (PS-802-RX2-24) paired with a Uni-match automatic water feeder. They are both 24V.

I measured the voltage on the N and W terminals from the LWCO to the water feeder. The voltage varied between 10.5V - 12V when the water is above the LWCO level and the low water light is off. Once I drained the water to below the LWCO level and the call for water signal goes out from LWCO to the feeder, the voltage drops to 0.003V. Measuring between the H and W terminals I get about 3V

My question is what is the voltage that I should measure coming from LWCO to the feeder? In my mind it should be 0V when it is closed and 24V when it is open calling for water but I was a bit stumped to find the opposite. I check this on two other machines in the building and they all have the same voltage when open and closed.

Jamie Hall

Remember that an LWCO, like a pressuretrol or a thermostat, is a switch, not a voltage source. What you measured was a closed switch, which should tell the automatic feeder that water is needed.

A thermostat is also a simple switch, as far as the system is concerned, not a voltage source. Closed switch = call for heat.

There should be other terminals on the LWCO which open at a lower level which are in the burner safety circuit.

petec88

Thank you for that reminder, was going off the rails there for a bit.

Looking at the wiring diagram from the LWCO to the water feeder, it seems N is the neutral from the transformer and H is the hot wire. Couldn't quite figure out what the W is for. Is that the wire that carries the signal to the water feeder to tell it to turn on and off?

Trying to see if there is a way to bypass or jump the signal from LWCO to the water feeder similar to how one might jump the wires from the thermostat to force a call for heath. Hoping to use it as a way of elimination to determine whether it's an issue with the LWCO sending a signal to the water feeder.

Joseph_4

W is the alarm terminal or as u stated the one that sends message to feeder to feed

petec88

Thank you Joseph. Is there a way to "jump" a signal to the water feeder?

The PS802 currently cuts-off the boiler when the water level is below the threshold and the low water indicator comes on. However, the feeder is not feeding (and the green light on the feeder does not come on). Trying to find a way to force a "feed" signal to the auto water feeder to determine whether it's the feeder I should spend my time diagnosing or the LWCO unit. Thank you!

EdTheHeaterMan

Jump W to C on the PS 802, to test the feeder, but you should read this.

On the PS 802, there are terminals that are marked N and H. that is where you connect a 24V transformer to power the control. If you are using a standard transformer independent of all other controls similar to a Honeywell AT72D You should choose the R terminal of the transformer to connect to the H terminal on the PS 802. I do this because every once in a while there is a 24V transformer that has the C terminal connected to the metal case as a ground. Not all do this, (most don't) but if you get in the habit of using R as the power and C as the return path or common, you will avoid confusion and possibly letting the smoke out of the transformer.

That said, You would then connect C of the transformer to N on the PS 802.

Your system may not be connected to an independent transformer, but connected to the transformer that operates the gas valve. So be careful to verify that you have the proper wire from the equipment transformer. Look for the one on the diagram marked C, Common, or the one that connects directly from the gas valve to the transformer. That is usually the Common or C terminal. If you have electronic ignition on your gas boiler, this becomes very important in the flame sensing circuit. All the auxiliary controls must all use the same terminal or wire from the transformer as the Common or C (or N on the PS 802 and the water feed)

If you mix and match the C or Common or N to different sides of the transformer, on the same heater, there WILL BE a smoked control somewhere.

Now with that all cleared up, the internal wiring diagram of the PS 802 indicated the C (different C than the transformer) is common to the normally open B and the normally closed W terminals of the SPDT switch in the PS 802. Since closing B and C are supposed to turn on the water feed... if you were to put a Jumper from B to C in the PS 802 you should get power to start the water feeder.


The water feeder may have a time limit on the operation. It is usually adjustable. This timer keeps the feeder from overfilling the boiler in anticipation of condensate returning to the boiler at some future point in the cycle. The fact that the feeder valve is not open to feed water when voltage is applied to the B and C terminals on the water feed, do not necessarily mean the feeder is defective. It may be on a delay or "DWELL/FEED" off-cycle.

If the boiler is not receiving enough makeup water causing a no heat condition, then you may need to adjust the "DWELL/FEED" timing accordingly.

BTW. 5 minutes is the longest time you should wait for the water feed to cycle thru the DWELL/FEED cycle. The LWCO may also have a time delay the will add wait time.

petec88

Thank you for the advice. Went back out today and realized I was measuring the wrong terminals yesterday. Instead of measuring H and N, I was measuring W and H which resulted in the 10V. Measured the H and N at both the LWCO and feeder and they are both at 27V (same as the output at the 24V transformer).

When the LWCO turn on, it wasn't opening the circuit and giving the voltage to the feeder as it should. It was only giving a reading of 10V with the LW light on. I took Ed's advice and jumped the C and W, the feeder turned on after a 1 minute delay.

I believe all the wiring from the PS802 to the uni-match WF2-U24 is correct. It has a weird labeling of 1, 2, 3 on the water feeder rather than W, H, N that I normally see and I couldn't find any materials that referenced the 1, 2, and 3. Currently, 1 is wired to W, 2 is to N and 3 is to H.

Thank you everyone for their help and support.

petec88

Just a final quick update. It was the Relay on the LWCO board that wasn't working and wasn't sending signal to the water feeder. Swapped out the $10 relay and everything is working as it should