Here are some tips that I've learned over the years for cleaning and maintaining the DF520 boiler. Everything should be cleaned at least once a year. I think the best thing you can do for your boiler is to turn the aquastat down to its lowest setting and adjusting the coal feed and air accordingly, such as 4 feed/4 air with 2 minutes per half hour of timer setting. Or whatever your personal preference below those settings.
The second best option would be as follows:
Before shutting down the unit for the season, check the draft at the flue and at the fire door. The unit should be running for at least a minute and the boiler and flue pipe should be hot. A draft of negative .04-.05 should be read at the breech in the flue pipe and a draft of negative .01-.03 should be read at the fire door. This will indicated that the draft damper is properly set and the air setting on the stoker is properly set. A good draft at the breech and a poor draft at the fire door can indicate too much air at the blower. A good draft will indicate that the boiler and base are generally sealed properly and the chimney is producing good draft. There are many places where draft can be lost due to bad rope gaskets, door seals, or poor boiler putty at the three base covers.
1. Turn off the electrical supply to the unit.
2. Remove the three baffles in the rear of the boiler. The cast iron baffle should be flat and hanging in V grooves on both left and right sides at the inside rear of the boiler.
The two steel baffles are hanging on hooks, 4 per baffle, underneath the cast iron baffle.
3. Use a soft wire brush to clean all the surfaces behind the removed baffles. Hard scale deposits may require a scraper, but be careful not to gouge the steel surfaces. Removing ash and scale greatly increases the transfer of heat to the water jacket. Replacing a warped iron baffle will direct the fire's heat to the water jacket instead of allowing it to escape up the chimney. Excessive firing of the boiler or, due to large heating needs, can warp the iron baffle, but generally, they warp from normal wear and tear. A large annual coal usage will wear out a baffle faster than low annual coal usage.
4. Replace the baffles.
5. Clean the rest of the interior of the boiler in like manner.
6. Clean all coal and ash from the burning pot. Carefully check the worm flights at the bottom of the pot. If they have sharp, knife-like edges, the worm is worn out and should be replaced. The outer edges of a worm flight should be about 1/8" flat or slightly rounded. Generally, a worm will last 20 years under normal usage.
From underneath, grab hold of the worm shaft where it exits the pot. It should not move up, down or sideways more than 1/16". Excess movement reveals that there is too much play between the worm bushing (mounted on the worm shaft by a pin) and the gooseneck bushing. Either or both bushings may need replacement and are available separately. Shown below are new bushings.
7. Use a drill bit or ice pick to clean through every hole in the burner plates. Remove all ash from the holes. Check for any cracked or warped plates. Replace any bad plates.
8. From underneath, check the operation of the clean-out cover. With the clean-out lever fully inward, towards the base, the cover should completely cover the square openings in the gooseneck. With the clean-out lever pulled fully away from the base, the cover should move to open the square openings in the gooseneck. Part of daily routine should be to open the clean-out cover for 15 seconds, with the clean-out lever, while the stoker fan is running, to empty all the coal fines that accumulate in the bottom of the pot.
9. Remove the shoulder bolt that attaches the clean-out rod "eye" to the clean-out cover and fully open the clean-out cover. If the cover isn't fully closing or opening, the "eye", shown below, can be threaded inward or outward to adjust the movement of the cover. It's more important to have the cover fully closed.
Use a small brush and clean the ash off the underside of the burner plates. Re-install the eye and shoulder bolt, using Never Seize on the threads of the shoulder bolt.
10. Clean the rest of the ash from around the sides of the base and in the ash can area of the base.
11. Remove the flue pipe and clean the flue pipe, as necessary, and leave it unattached. Cap off the end of the flue pipe.
12. Brush or vacuum all the ash from the rear section of the base, through the flue outlet and then cap the flue outlet. Make sure to hook up the flue pipe before starting the unit for the Winter.
13. Check the operation of the gear drive. The drive pawl on the top of the drive can have accumulated dust and grime which would make it sticky. Remove the nut and bolt and clean with a suitable cleaner to remove all grime. Do not oil the drive pawl. T?he top row shows the check pawl parts and the bottom row show the drive pawl parts. Both should move without resistance and neither is oiled.
There are 3 oil ports on the gear drive. One can be seen when looking straight down from the top of the unit. It is located in the bearing bracket, part number 9433763, shown in the picture below. It lubricates the clutch shaft. It cannot be over-oiled. I would use a few drops of 90W gear oil every month, or at least annually.
The other two oil ports are on the connecting rod ends, part number 9443087. Both are easily seen. I would add a drop of 90W gear oil every month or at least annually.
The gear box used on all the latest units is lifetime lubricated with 90W synthetic gear oil. The old iron gearbox with the 1/8" street elbow installed, uses 20W machine oil and is filled to the point of overflowing the elbow.
14. Check the oil reservoir, part number 9441329, for contaminated oil. If dirty, remove and replace with 90W gear oil. Only fill to the level where the bottom teeth of the large gear, part number 9433944, are covered by about 1/4" of oil.
15. Oil the stoker motor according to the manufacturer's specifications.
16. On the older boiler units, from around year 2000 and back, check the domestic water coil gasket for leakage. These coils are directly against the boiler and secured with nuts only. (Newer coils are mounted to an extended flange and extend out the back of the boiler by about 3 inches. They are secured by nuts AND bolts.) It is necessary to remove some of the boiler jacket to do this properly. Leakage around the gasket and the resulting rust/oxidation is probably the number one reason for boiler failure. Steel patch plates are available to repair the damaged rear of the boiler, but with annual inspection and replacing a failing coil gasket, repair of the boiler should never be necessary. Signs of gasket failure are rust stains around the coil perimeter. You may never see any sign of a leak while the boiler is hot because the water will evaporate immediately and the damage will be silent. An actual water leak may occur when the boiler is shut down for the Summer and the boiler is cold.
Each year, the coil gasket should be checked for leakage and rust stains. Replace any hard gasket any time there is evidence of rust around the lower part of the coil. Gently tighten each nut around the coil. I would keep the torque to 10-15 foot pounds per nut. If the coil is leaking and the gasket is soft, it should only be necessary to snug up the nuts. If it was my boiler, I would remove and reinstall the nuts, one at a time, and use Never Seize on each stud. DO NOT overtighten the nuts. The gasket should slightly bulge. Overtightening the nuts will cause the gasket to tear.
Coil gaskets should easily last 10 years and probably much longer, but they still need to be checked annually.
Late model coils with an extended flange and secured with nuts and bolts are easily checked for leakage. Do not overtighten the nuts.
Any older boiler can be converted to the newer style extended flange type with a patch plate, extended coil pouch, and newer style coil.
17. If ANY leaks are found at pipe fittings, coil gasket, or anywhere else in the system, they must be fixed immediately. Adding oxygenated water to any boiler system because of leaks will reduce the life of the boiler. There are many efm coal boilers still in daily use from the 1950's and the easiest way to shorten the life of a boiler is to have water leaks.
18. Check the coal feed pipes for any holes or rusting. Rusted sections of pipe can cause binding in the feed system and breakage of sheer pins. Stainless steel pipes are desirable for high usage of coal.
19. Finally, it's a good idea to keep the inside of the boiler dry. Since the unit will not be producing any heat, consider using a light bulb or some other safe source of heat to keep the boiler warm and dry inside.