Hello, I recently installed an oil boiler … for the most part it is working fine.

By code I need to install a low water cutoff switch (LWCO) that will interrupt power to the boiler. Ideally, it should cut off all power to the boiler, but minimally it should prevent the burner from firing when a low water situation is sensed. I have the switch installed and it appears to sense low-water properly, but I have an issue getting it to work in my setup.

The LWCO can be wired directly into main to supply/deny up to 115v AC @ 5.8A. Problem is, my house circuit is 115v @ 15A, and I doubt that 5.8A is within the power draw for all my boiler equipment. The LWCO can also be wired to simply interrupt any 12v, 24v, and 115v supply (assuming the limitations above). I found that it is not sufficient simply interrupt the 24v zone valves, because the Aquastat has min/max temperatures configured and will fire the burner independently of any call for heat.

So as I see it, I have 2 options:
- My Riello F3 burner is rated at approx 115v AC @ 2.5A draw. So, I should be able to wire the LWCO with a 5A fuse to directly interrupt burner line power. In a low water situation, I’ll probably damage the circulation pump, but at least the burner will not cause a fire or crack the boiler.
- Find some sort of way to convert a simple on/off switch to control 115v AC @ 15A.

I would prefer #2 above. I’m assuming I would need some kind of powered device with a high voltage relay that can handle this power draw.

In my setup I have line voltage coming to job box A where the LWCO is connected. Line voltage then goes to job box B where all boiler equipment (aquastat, pump, 24v zone transformer, etc.) is connected. So ideally, I would like some kind of device that I can install on or near job box A that when tripped by the LWCO simple contact relay, will prevent all power from going to job box B. LWCO is normally closed relay that opens on low-water condition.

Any advice?

Thanks!

 

What electrical requirements are on the boiler nameplate?

 

If I am reading you right, the 5.8A is the rating on the LWCO switch. (IE: printed on the side)
The 5.8A is the max that the switch can carry. Your boiler is 2.5A. So putting the switch in series on the line coming in to the boiler should work just fine.
The LWCO switch does not need to have the same rating as the circuit. It only needs to have a rating greater than the load to be served.
If your boiler drew say, 10 amps, then you would have to find another way to hook it up.

 

Yes, the 5.8A is the rating of the switch. So in this respect, it should be sufficient to interrupt power to the burner by itself.

I would prefer some kind of device that I can hang off of this LWCO to interrupt power to all of the boiler devices. I'll have to add all of this up, but I suspect that the requirements of the burner, aquastat, 24v transformer / zone valves, and pump running all at the same time is more than 5.8A

 

Unless the burner is an induced draft, it should have almost no draw. The aquastat is just another switch off the transformer. The zone valves are also off the transformer. Unless I'm missing something, the only draw you should have is the total of the 24v transformer and the water pump.

 

No, it's a bit more complex than that.

The burner has an oil pump and a blower motor and the specs say average draw is about 2.8A.

The aquastat feeds directly off of main ... it is a computer board, but probably doesn't do much itself. It does however directly supply power to the pump and the burner. The zone valves are the only item that sits on the 24v transformer. I don't think they use much, but when a thermostat calls for heat the zone valve motor is energized the entire time.

In any case I'll probably need to use the LWCO to control the burner directly, unless I can find some device with a relay I can trip to handle all of the boiler power.

 

The LWCO must be connected to the burner unit not the circuating pump from my past experince with larger boilers I know one of my freind he is HVAC contractor and he told me the regulations with the LWCO.

And your LWCO switch rated at 5.8 amp that is fine for yiour burner pump the circuation pump can be wired seperated the reason you can able keep the circuating pump running.

If you need more details I can able get ahold one of our HVAC guy he can be more than willing to help you with this sistuation and I can ping him anytime if you want to he is on this forum as well.

Merci.
Marc

 

I think it should be fine to just interrupt the burner with he LWCO. To ease your fears about burning out the circulation pump it should have a thermal overload switch or fuse built-in that will cut off power if the pump runs dry and over heats.

 

French277V asked me to take a look at this thread since HVAC is my specialty.

James: Your total load would not likely exceed the 5.8 amp rating of the LWCO. The aquastat is only consuming enough current to power it's transformer, the transformer for the zone valves (presuming a 40 VA transformer) might pull a little over an amp, the circulator (presuming a Taco 007 or similar) will draw less than 1 amp. All that being said, you can bring power from the service switch, to the LWCO, then to the aquastat (which in turn powers the burner & circulator). No need to be concerned about the zone valves' transformer. The zone valves don't care if they are wet or dry. Hope all this helps.

 

Thanks Grady for comming over in here and help to clear up the matter here.

Merci.
Marc