Hello everyone. I ran into a problem with my oil burner yesterday. I have a hot water baseboard system that includes a low water cutoff, an aquastat relay, and a Taco 4 zone switching relay. The house was a bit chilly yesterday so I went to check on my furnace and I found that the low water cutoff had sprung a water leak. It got into the electronics end of it and completely fried it to the point that the 120V hot wire was burnt off the circuit board. Luckily I found one locally and changed it out easily enough, but the burner still will not fire. Now I am wondering if the aquastat relay and/or switching relay are also bad.

The way this is wired is the 24v "isolated end switch" of the switching relay runs into the low water cutoff. The "TT" line of the aquastat relay then runs into the furnace's "TT" input. There is a 110V line tapped off of the switching relay that comes into the aquastat. That input is then tapped to power the low water cutoff, and of course the output of the aquastat goes to the furnace.

How can I test the aquastat relay and the switching relay to see if they are working properly, and is there something else I should check to see if it is functioning also? Thank you kindly for your help!

 

make / model of boiler?

make / model of aquastat?

make / model of LWCO?

make / model / function of the switching relay?

 

I dont know the model of the boiler off hand but it is a Beckett

Aquastat - Honeywell L8148A

LWCO - Safgard 1150

Switching relay - Taco SR504. The 4 zone thermostats run into it and trigger 110V to the 4 circulator pumps, and the isolated end switch runs into the low water cutoff.

 

Only the oil burner is a Beckett, the boiler isn't manufactured by them, but not really important to know as long as controls are known.

To what terminals is the endswitch wired?

You also have 120VAC wired to the H and N terminals, obviously.

Is the green LED on the new LWCO lit? and the red one OFF? and does the red one light when you press the 'test' button?

What wires are connected to the "CUT OFF" terminals? Where do they go?

I don't understand what you are saying here. The T T terminals of the aquastat generally ARE the T T terminals of the BOILER.

It sounds to me as if your system is not wired the way we normally see them wired.

With the 1150 LWCO, it is normally wired so that it cuts off the AC POWER to the rest of the boiler system. It CAN be wired to cut off the 24VAC signals, and it sounds as if that's how yours is done, but from your description, I can't visualize it at all.

 

Can you take pictures that clearly show the wiring?

I need to have an exact understanding of how your system is wired if I'm to be able to help...

 

The end switch is what is hooked to the low water cutoff's "cutoff" wires.

The LED's on the new LWCO are functioning as they should, green on and amber when I hit the test button.

I took a few pics, I hope they help. The 1st one is the zone switch. It shows the isolated end switch wire, which goes to the LWCO's "cutoff" wires, as shown in pic #2.

The last two are of the aquastat. You will notice a brown 24v wire, which runs to the TT terminals of the boiler. I hope this is somewhat helpful. Thank you for your desire to help!

 

Sorry, still confused. This isn't making sense to me!

You say that there are 2 wires from the Taco panel endswitch, and that these go to the LWCO "Cutoff" terminals?

This is the first thing I don't 'get'. The 'cutoff' terminals are simply another 'switch'.

Wiring the endswitch to the cutoff terminals accomplishes nothing at all. You've got a switch in parallel with a switch, and nothing is communicating to the boiler to 'turn on'. Somehow that endswitch from the Taco panel needs to 'talk' to the boiler controls.

Next I don't get:

That brown wire is coming from the T T terminals of the aquastat, and going where? To the T T terminals of the BOILER? As I said earlier, the T T terminals of the aquastat ARE, or SHOULD BE, the T T terminals of the boiler.

Where exactly on the boiler is this 'other' set of T T terminals? You didn't picture that, did you?

In this case what I think you are saying is that you've got two sets of inputs connected in parallel. This again will accomplish nothing (except perhaps burn out a transformer if there is also one in the boiler on the 'other' control not pictured).

Did you by any chance take pictures of the wiring before you removed the LWCO? Or label the wires, or sketch a diagram? And you are absolutely 100% certain that you wired it EXACTLY the same when you put it back together?

 

I did not take pictures. There is a slim possibility I could have mixed end switch wire to the LWCO and the aquastat wire to the TT on the boiler, only because I had them disconnected at the same time. I am fairly sure I was careful to identify what wire went where, but in my state of duress I can't say for sure I am correct.

Would it make more sense to have a 24V wire from the end switch to the aquastat, and one from the LWCO to the TT on the boiler?

This is the only way I could have possibly messed up any wiring. If this still makes no sense, please advise on how I can wire this to work, or again how can I test the other switches/components to be sure they are not part of the problem.

 

Chris, I have some ideas about what happened, and along the lines that you are saying... but you need to answer the questions I ask:

It might, but this goes back to exactly where this "TT on the boiler" actually IS.

Because without having a FULL EXACTLY CORRECT picture of how the system is being controlled, I can't suggest my ideas.

 

Wait... I think I may know what you are talking about.

When you say "TT on the BOILER" or "FURNACE" as you originally called it,

Do you mean the TT TERMINALS on the OIL BURNER CONTROL? The terminals on the square control box on top of the OIL BURNER? above the MOTOR?

I think you do mean this... the misunderstanding is in the words being used, and why MORE PICTURES are better then fewer.

 

If the previous post is correct, that you mean the BURNER T T Terminals, then YES, you mixed them up.

The ENDSWITCH in the TACO panel wires to the T T terminals in the AQUASTAT.

The CUTOFF in the LWCO should be wired to the T T terminals on the BURNER CONTROL.

But do NOT do this if you are not certain, or understand what I mean by BURNER CONTROL... there is probably a RED RESET button on top of that control.

I would feel more comfortable about telling you to do this if I could see a picture.

I need to cut outta here though and don't want you to be without heat if you don't have to be.

 

By the way, technically, this is NOT the 'proper' way to wire the controls, but it will work, and in order to do this the 'right way', you need to do some significant re-wiring.

There IS another wiring alternative which I'll tell you about tomorrow.

 

Trooper,

That is in fact my burner control. I wired it as you said and she fired right up! I can't believe I made such a simple mistake. What it comes down to is I didn't understand the path the signal should be traveling and didn't know what was an input and output. If it isn't too much trouble would you be kind enough to explain this to me?

 

The majority of boilers produced these days use a Honeywell aquastat.

In the most basic of systems, single zone, the user would simply wire his thermostat to the T T terminals of the Honeywell aquastat. So in the vast majority of cases, the T T on the aquastat is considered the 'input'.

The thermostat is basically nothing but a 'switch', a 'contact closure'. When a connection is made between the T T terminals of an aquastat, the system will run.

In a multi-zone system, inputs can come from multiple sources... the Taco panel will accept these multiple input sources (thermostats, water heaters, etc) and produce from them a single contact closure OUTPUT that will close when ANY of the sources call for heat... this is the ENDSWITCH, and it's nothing more than a 'contact closure', a 'switch', just the same function as a thermostat.

When this endswitch is wired to the T T input on the aquastat, any one or more of the multiple inputs can fire the boiler.

Your system's LWCO is wired to a seldom used (on HOT WATER boilers) set of contacts on the BURNER PRIMARY CONTROL. This is another set of T T terminals, another INPUT.

The oil burner can be fired in multiple ways. USUALLY, the T T terminals on the BURNER PRIMARY CONTROL are JUMPERED with a small piece of wire. The burner is controlled in this case by whether or not the AQUASTAT sends it 120VAC power.

BUT, if the aquastat sends the signal to the burner to fire, and the T T terminals on the primary control are OPEN, the burner will not fire.

Next up is your LWCO. Not all systems have them. The "CUTOFF" terminals in your LWCO are another set of 'contacts', another 'switch'. When water level is detected as 'normal', this set of contacts is CLOSED. When wired to your burner control T T terminals, it will ENABLE the burner to fire when a command comes from the aquastat to do so.

When water level is detected as LOW, the CUTOFF contacts OPEN and DISABLE the burner from firing, even if the aquastat is calling for heat.

So that's pretty much it... to summarize:

When ANY thermostat calls for heat

Taco endswitch closes and calls

Aquastat to fire the burner and turn on the pump.

Burner will only fire if LWCO permits it to by closing CUTOFF terminals.

 

The reason that the way your LWCO is not wired in the best way is because the only thing that will be 'cut off' in the event of low water is your burner.

It WILL protect against the most obvious cause of damage from low water... a cracked boiler, house fire, boiler explosion...

But, if the boiler is low on water, and there is a heat call from a thermostat, the zone valves will be open, and the pump will be running continuously until someone notices.

Zone valves are made for INTERMITTENT duty. They aren't intended to be held open for hours and hours. The electric motors in many models will overheat and be damaged.

Modern circulator pumps are lubricated and cooled by the water they are pumping. If they are left to run dry, they will be damaged.

To be most effective, an LWCO should cut off power to the boiler in such a way that the zone valves can't open, and the pumps can't run, in ADDITION to cutting off the burner.

 

Thank you SO much for shedding light on this! It does make sense when you spell it all out, but trying to guess and figure it out myself wasn't going to happen. You've been a tremendous help, I can't possibly thank you enough!