flue temperature sensor interlock device

Please point me in the right direction. I have a 20 year old Keystoker boiler, central heat, not stove.

I am looking for a temperature sensor interlock device I can install in the metal flue pipe, below the diverter, that will monitor the flue temp, stay closed when hot, and keep the burner running.

When the fire goes out, it cools, opens contacts, and shuts down the burner, before it can make a huge mess by continually feeding coal.

This is a heat sensor that controls the 120v ac supply to the burner. Opens and kills the power when the fire goes out and cools the flue.

Any advice on doing this ?

What are they called, and where do I get one ?

What you are looking for is a bi-metalic snap action switch. The best know devices are called "Klixon" switches. They are trademarked name by Texas Instruments. See: http://www.sensata.com/ for more than you will ever want to know about Klixon switches.

You will need to select a switch that is normally closed and opens on temperature fall. I'll suggest a switch with a pair of mounting tabs to attach it to the flue pipe with sheet metal screws. Be sure to select a switch with leads so you don't have any exposed contacts. You will need to know the desired switch temperature and differential. Klixon 20420 & 20425 Series in surface mount version would be an appropriate choice.

Hello mn91, welcome to the forum. I have a concern with your proposed flue-temp switch. I don't know what are normal temperatures in the flue of your boiler, but I think you could get into a situation where the boiler is just idling, burning just enough of a fire to keep the fire going, then if the house calls for heat, starts the circulator pumps running which brings lots of cool or cold water into the boiler, couldn't the flue temps drop enough that the temp sensor would think the fire has gone out, even though it hasn't? And the sensor would open, not allowing the burner to run?

If you have experienced the fire going out because of low demand on the boiler during warm days, your burner should have a timer on it that will activate for a minute or two every 30 minutes or hour and push coal onto the grate,and run the combustion blower to keep the fire going in an 'idle' or 'pilot' condition.

Maybe your older Keystoker doesn't have a keep-lit timer? Does your burner have one motor running the blower and the pusher mechanism? Sometimes during warm weather the chimney draft is too low to keep enough air pulled through the grate to keep a minimum fire burning. Some people have hooked up a second 'auxilary' blower that is aimed at the main blower inlet, this runs full time, forcing a small amount of air through the grate augmenting the lack of draft from the chimney.

If you describe your situation that you experienced and are trying to prevent, maybe we can help better. Describe your chimeny too.

Greg L.

Do you have any photos of the unit installed? Maybe post one in the photos of your stove thread or with your reply..

Hello mn91311, I am guessing that you are using your boiler year round for hot water during the summer. I am guessing that you only loose fire in the summer on hot days. This is the curse of the Keystoker. You can add more time on the timer and now you have a hot boiler and if it is in the basement a hot basement as well.

If you look on the Keystoker web site you will notice on their stoker pictures that they have added a small second blower under the stoker motor and blower. This small blower is wired to be always on. Keystoker claims that their new units with this second blower do not go out during the summer. Most of the older stokers can be fitted with this second blower via an adapter plate and a hole must be cut into the blower housing to let the air in under the grate. Keystoker claims that with this second blower there is no more unburned coal in the ash and that you could burn up to a ton less coal per year.

I have an older Keystoker I installed last year. It has no second blower. I bought a blower and adapter from Keystoker for $150. I will be upgrading my boiler sometime this year and will be sure to post some results as I get them in. This is the first summer of burning for me with this boiler and I had the fire go out the first hot days we had the last week of May. After that I added 15 seconds of time on the timer and reduced coal feed by 1 turn and it has held fire ever since then and boiler temp is about 150-160 burning 16-17 pounds a day. This week should be a good test to see if it can hold fire!

I have considered doing exactly what you want to do but have changed my mind. If I feel that the upgrade with the second blower is 99.99% effective at keeping the fire going I will then install some kind of battery backup to keep it working during power outages and also give the boat batteries a job when not needed for fishing.

If you go with the automatic cutoff switch the only two issues I could possibly see would be getting the temperature setting right and maybe the need for an override switch for starting the fire when it is out so you can run the blower.

Whatever you do please let us know how you make out. Good luck.

I don't know the Keystoker boiler at all. But if there is a way to mount a thermocouple that would sense ash temperature you could use it and a PID thermocouple controller to turn on the combustion blower. Similar to what AHS does. There would be several requirements on the probe mounting. It couldn't come in contact the the hot coals at least not all of them. An occasional dying coal would be ok. Shaking or adding coal shouldn't move or bend the probe. Ebay prices for a new controller and thermocouple would be less than $100. Considerably less if the thermocouple that comes with the made in China PID controllers would work.

Here is an example of a simple Snap switch you could hook up in series with your stoker, the flue temp would over 110 degs. the contacts are closed, if it cools down below that, it would open. Something like that anyway.

I know what you mean, if we get a power outage (more than an hour or so), our stoker would go out and if the flames go out, it will still continue to run and push coal without burning.

http://cgi.ebay.com/New-Selco-CA115-Tem ... dZViewItem

I'm pretty sure Dave means the power goes out, the fire dies due to lack of combustion air, then the power comes back on, and THEN the pusher fills the ash pan with unburnt coal.

I'm thinking a battery backup for power outages would be a good idea. Small inverters are cheap, and I know Dave has a few batteries not in use during the winter. The relays and electronics wouldn't be too tough to set up either.

Greg L

The theme of battery backup operation occurs over and over. I personally don't have the need for such a system because I have a whole house capable generator. There are design issues you should be aware of in battery backup systems. We are all looking at the inexpensive UPS products sold for computers. They are not appropriate for running inductive loads like motors. The square wave or stepped sine wave they produce causes high voltage spikes, the spikes over time will damage the motor winding insulation. Realize enamel insulation is just an improved form of varnish. The spikes puncture the insulation with holes and you get a direct short. How long is "over time" is unknown. Could be hours, months or years. The UPS inverters don't like motor loads either. They fail for the same reasons, high voltage spikes. The UPS powers computer systems reliability because most computer electronics use switching type power supplies which first rectify the incoming power to direct current (DC). This eliminates all the spikes.

If operation of your coal appliance without utility supplied power is important to you I would design a system from scratch. Select a drive motor that is a DC motor, or a universal AC/DC motor. Your blower motor may be a universal motor already. The point is you want DC power to be able to run the motor. This DC power will come from the batteries. The most reliable systems run the load from the batteries all the time. Utility power simple keeps on charging the batteries all the time. That way the batteries are always fully charged and the system will continue to hum away when the utility power goes off. No switchover process needed. You size the battery for the amp hours needed. If you base your design on 12 volt lead acid type batteries you have a lot of choices of batteries and battery configurations. For very long power outages you could even recharge batteries with your automobile.

The switch would cut out the stoker if the fire dies down or out to a certain temp. If there is still a fire, the power comes back on, the flue would heat back up, activating the switch, turning the stoker back on. If the fire was out, the stoker would not activate since the flue temp was below the setpoint. The rest of the stove would power back up, but at least it wouldn't continue to waste coal if there was no flame.
See attached for a BASIC schematic.

Yes, mine runs in series from the AC to the UPS to the Stove.
It is a computer power supply backup (800-1000watts?), runs approx. 20mins, but putting a car battery on it, so it should last longer. We've only had a couple of outages, one was over 2 hours. Didn't matter, the furnance didn't come on either...got a bit chilly in the house.!!

How about a big car or marine battery and with an inverter?

You would have one or more batteries on trickle charge. If your power goes out for a while and your battery starts to run low, you use your car or truck’s alternator to charge up your dead batteries. Or you even take your car battery out and swap them. I don’t know if car batteries are designed to run until dead like marine batteries are. That could shorten their life, same with your alternator. If your trying to get by in an ice storm, that’s the least of your worries.

I had plans of doing this, for my blower fans. However like Yanche I have a generator. I found a second hand 5000 watt generator, which should be enough for my essentials. I'm just need to tie it into my circuit break with a manual switch. This solves the biggest fear for a girlie man.

coal_kid wrote:I'm just need to tie it into my circuit break with a manual switch. This solves the biggest fear for a girlie man.

My whole house generator isn't yet wired in with a transfer switch. What I do have is a feed line from the generator connected to a 60 amp two pole circuit breaker. The circuit breaker is NOT normally connected to anything. It's just coiled up. When I need to use the generator I FIRST turn off the main circuit breaker. Then I remove an existing two pole breaker, the one that feeds my air compressor. I just pry it out and let it dangle on the wires. Then I install the breaker from the generator in its place. This will back feed the panel and get juice to the entire house. I seldom loose utility power and it works for me. An example of "There's nothing as permanent as a temporary fix that works". To install the automatic transfer switch that came with the generator according to the code book would take more time and money than I'm willing to invest.