Stoker Outfires and Settings Suggestions to Prevent Them

A man who has been having constant outfires in his efm 520, over the past year or so, has finally solved the problem.

His experiments led him to use a 15 minute timer and running the stoker 1 1/2 minutes every 15 minutes. The feed rate was set at 4 teeth and the air at 3. With a short run time, the boiler wasn't spiking much, if at all, in water temperature variation.

Although final settings vary between units, it's worth a try.

Some other common reasons for outfires:

Outfires
1. A stoker-fired boiler is different from an oil,
gas or electric unit in that the fire must be maintained
by periodic running of the stoker, even
though there is no call for heat by the thermostat
or operating aquastat. This is accomplished by
the timer. A normal setting on the timer is 2 minutes
of stoker operation per ½ hour. This is a
suggested start and times may have to be varied
to suit installation conditions and the time of year.
Due to the wide range in the quality of coal available,
a timer setting of 2 minutes per hour might
produce an acceptable burn. It’s an experimental
process of timer run-times, air and feed settings,
with the two main objectives being a
proper ash ring (2 inches) and a fire that does
not burn deeply into the bottom of the pot. If
the quality of the coal remains consistent
throughout the year, the settings can be
recorded. There may be different settings for the
warmer months than for the colder months.
Record both settings.
2. An outfire in the stoker is a more prevalent
condition during the summer months. It can
happen even though you find nothing wrong with
the stoker mechaninism. The following (A thru C)
are some conditions which can cause an outfire.
These are situations that start to develop where
there is no apparent explanation. For other situations,
refer to the service check list.
A. Feed rate too high for summer operation:
In this situation, where the stoker is maintaining
8
boiler water temperature for domestic hot water
and there is little domestic water draw, the boiler
water temperature can reach the high limit setting.
The high limit control overrides the timer,
not allowing the stoker to run and results in an
outfire. This occurs on a hot water system and
can be corrected by dropping the feed rate, raising
the high limit setting, lowering the operating
setting on the aquastat to create more of a temperature
spread between the operating and high
limit setting on the aquastat, and decreasing the
differential on the operating control.
The bypass piping, as shown in Fig. 7, is very
important in helping to alleviate this condition by
reducing stratification of the water in the boiler.
Removing insulation from the boiler will also
help.
Note when adjusting the aquastat:
The L8124A or L7224A aquastat, furnished with
this unit, has three settings.
1. The High Limit Setting: This shuts the stoker
“off” when the water temperature reaches the
temperature setting. It overrides all other controls.
2. The Operating Setting (Low Limit): This setting
maintains the boiler water temperature and
shuts off the stoker when the water temperature
reaches the setting, but not if there is a call for
heat.
3. The Differential Setting: This setting determines
when the stoker will be fired, as the boiler
water temperature cools. For example: If the
operating control is set at 160 degrees, with a 10
degree differential, the stoker will come on at 150
degrees (water temperature) and shut off at 160
degrees (water temperature). The thermostat or
timer can override this setting, but cannot override
the high limit setting.
B. Loss of draft:
This can occur during hot, humid summer
weather, with low fire in the burner. Changing the
number of minutes of operation per half-hour,
increasing slightly the coal feed and air settings
may help. Thoroughly cleaning the boiler, flue
pipe and chimney, to remove fly ash buildup will
also help. Be sure the fire and ash pit doors are
closed tightly. Check that the clean-out lever is
fully pushed back towards the boiler and that the
clean-out cover plate openings are fully closed.
Check that all openings, where outside air could
infiltrate the boiler base, are sealed.
C. Too much draft:
This is most apt to occur during cold, windy
weather where there is no barometric draft control
in the stack. In this situation, the fire continues
to burn, even though the stoker is not running.
Addition of a barometric control, or proper
adjustment of the barometric control, if present,
will help. Exhaust fans can also cause this problem
by drawing air down the chimney, through
the burner and out of the fan housing inlet. This
can be corrected by providing adequate outside
air intake openings for both the stoker and the
exhaust fan or discontinuing the use of the
exhaust fan.

Stoker:

Any idea where he got his timer that runs every 15 minutes?

Manny

C8835 Intermatic timer, available from Grainger, or us.

Honeywell offered the timers in both 1 hour/ 1/2 hour and 1/2 hour 1/4hour units . Can't remember the timer part numbers. I have both in the shop. I'll check numbers and post later.

My honeywell timer is a one-hour timer.. on the wheel, you can add or remove the 'pins' that trigger the timer as often or wherever you want... I could put a 'pin' every 15 minutes if I wanted to.. or like I have it now, two pins in one spot, triggers the timer for a 2 minute burn once an hour.

You don't need to buy a new timer for a shorter interval,, only if you need a longer interval. At least with my brand/style of timer.

Greg L

My friend has a Honeywell timer with a 1 hour dial, he only has 2 on pins and 2 off pins, he would like to set his furnace to go at 15 minute intervals and is in need of additional on-off pins. Where can we find additional pins to accomplish this. Any help would be greatly appreciated.

I have a bunch extra pins. If they fit yours for the price of a postage stamp you can have some, just PM me & ask. That's a 3/8" wrench.