Frohling wiring

Check the directions, there may be a safety circuit that comes jumpered from the factory, that you can break with the 1 pole low water cut-off.

The Froling has a built in overheat thermostat that shuts the system down at 100c (212f) and cannot be reset until the temp drops to 77c (170f) and even then must be done manually.

When it shuts down due to overtemp, the circulator continues to run to cool the boiler and the primary and secondary air dampers go to 0% to make the firebox basically air tight and kill the fire.

The primary and secondary damper actuators both need electricity to close, if the low water cutoff tripped, the system would completly stop leaving the air supplies open, the remaining water would stop circulating and the fire would continue to burn.

Mine has no low water shut off and I don't think I would want one. I'm no pro and I may be wrong, but I would skip the low water cutoff.

If "Piker" is around, he would have the best answer or call your dealer.

We normally use a double pole RIB relay to tie in the safety circut. once water is proven, power is supplied to the second leg of the coil on the relay and the normally open contacts close supplying power to the boiler.

Lee has the answer for a 110v low water cutoff on a 220v boiler - DPST relay with the coil wired to your cutoff switch.

That having been said, there is no mention of a low water cutoff in the Froling installation manual, and I don't really see the absolute necessity for one. If low water happens when there is power to the boiler, the boiler will quickly overheat at which point the control on the froling, as Dave mentioned, will take care of things by closing combustion air off completely to the fire. The boiler will then have to be reset manually before the boiler goes back into heating mode.

The only time I see a need for a low water cutoff is in the event of a catastrophic boiler control failure that happens at the same time as a catastrophic piping disaster - say a runaway draft fan and a burst pipe that is bad enough to prevent the pressure reducing valve from replenishing the system. If this happens, a low water cutoff might be desirable, but the only way to achieve this type of protection while maintaining the normal operation of the controls under a low water scenario where the control on the boiler is working properly (ie shutting the dampers on overheat) would be to wire the low cutoff to the draft fan only. This might be a viable solution, but I would want to check with Tarm Biomass first to see if they would support such an endeavor. My guess is they too will suggest forgoing the installation of a low water cutoff.

As far as how the Froling reacts to a power outage... even if the primary and secondary dampers are open when the power goes out, the fire goes pretty low pretty quickly. As long as you have an adequate dump zone, the water inside the boiler will likely stay within reason. I have tested this several times here with our unit, and never had an issue... though to be honest I haven't tested this in a worst case scenario where the fire box is loaded up full and burning at its hottest point in the cycle... no sense in stretching the limit... I've taken it far enough to feel confident the system can handle whatever I throw at it. I suppose if there was a crazy overdraft you could have problems... which is why there is a clutch on the damper servos so that the home owner can close the dampers manually if necessary.

Hope this helps...

cheers

Yankee said:

Thanks for the reply. I talked to Tarm Biomass, and they have no requirement for either a low water cut-off, or a fire-matic cutoff. I did talk to Revision Heat, where I bought the boiler, and they said that if I wanted them to inspect the installation, then it needed to be up to "code". Maine code requires both. I have a relay coming, and and they sent a sample diagram for the relay wiring.
On another note, is there a 24v supply on the Frohling for the power out dump valve? I have a couple of other questions, but will post a new topic.

Tom

Click to expand...

The power out dump zone needs it's own 24v power supply. The power on dump zone is merely an aquastat wired in parallel to an existing heating zone.

I did not think about code requirements in Maine... I knew from my sales rep days that Maine is quite a bit more strict when it comes to solid fuel boilers than other states... that being the case, I would find out about tieing the low water cutoff into just the draft fan... by putting the whole boiler on the low water cutoff, you actually do away with some of the safety features that the boiler has integrated into it's controls... not sure if the code guys understand that or not...

cheers