In my last column, I ran down a shopping list of tools and instruments needed to carry out a preventive maintenance program on your fuel-fired heating equipment. Now, let's see how they'll be put to use. In setting up a preventive maintenance program, there are three issues to be dealt with:
- What do you check?
- How often do you check it?
- What results are you looking for?
Checking frequency recommendations are what I believe is a reasonable compromise between the needs of maintenance and production. Frankly, there is no single schedule that satisfies everyone's needs, but you should perform at least quarterly checks on most items unless your history indicates otherwise. If you check blower filters quarterly but find yourself being called out to replace or clean them every month, the equipment's telling you to step things up a bit.
- Examine the burner for signs of localized overheating such as discolored or blistered paint, or warped sheet-metal components. These are signs of internal damage or hot gas leaks in and around the burner.
- Check the firing tube for distortion, cracking, excessive oxidation or burned-out spots. If the burner has a refractory block, make sure it hasn't begun to lose pieces or crumble. Longitudinal cracks, by the way, are common in blocks made of castable refractory. As long as they don't open up, causing leaks or the loss of pieces, they're not a problem.
Combustion Air, Recirculating and Exhaust Fans
- Check fan motor amps to make sure they're not excessive for the horsepower consumption of the fan and to make sure all legs of a multiphase circuit are carrying their share of the load.
- Check for excessive fan vibration, a sign something might be going out of balance.
- Bearings -- if they're not sealed units, lubricate them.
- Pull the cover off the housing and inspect the fan wheel. If necessary, clean any accumulated dirt and fuzz off it -- that detracts from flow and pressure development. Check the hub screws for tightness before you button it back up. A once-a-year check is probably sufficient.
Burner Combustion Air
- With the equipment at its normal operating temperature, measure the air pressure drop across the burner at high and low fire.
- Check the blower inlet filter. Clean or replace it if necessary.
- If the burner has a motorized air control valve, shut the burner off and disconnect the linkage connecting the valve to its drive motor (be sure to mark the linkage so you can reassemble it where it was). Manually open and close the valve while feeling for any signs of binding or tightness. If it sticks, the shaft seal may be drying out or getting ready to seize, or there may be an object stuck in the valve. Don't laugh -- over the years, people have fished shop rags, work gloves and bottles out of air piping.
- Next, cycle the drive motor from high to low, watching it closely. If it seems to stick or stutter while it's traveling, find out why and fix it.
- Finally, reconnect the linkage and cycle the unit again. The motor and valve should travel smoothly from low to high and back. If they don't, the linkage between them may be misaligned or binding. Make sure the linkage swivels and pivots operate freely, too.
- With the equipment at its normal operating temperature, measure the gas pressure drop across the burner at high fire. You can also try to take a low fire reading, but in my experience, it's usually so low that it's virtually unreadable. (If your burner has a metering orifice in the gas line, it's usually preferable to reading a drop across the burner -- it tends to be more accurate.) Compare these to the manufacturer's specs and make a log of them.
- Check the gas pressure entering the control valve or proportioning regulator. Again, compare your reading with the manufacturer's recommendations.
- If your system has a motorized gas control valve, put it, the motor and the linkage through the same checks as mentioned above for air valves.
Temperature Control System
- Examine thermocouples for signs of overheating and damage, and run periodic calibration checks to make sure they're reporting accurately.
- Check the calibration of your temperature controller. This can be done with a run-up box, which generates a known millivolt signal. (For how to build a run-up box, see "Checking Your Heat Process On a Budget.") The readout of the controller is checked against the temperature corresponding to this millivoltage.
Go to "The Third Ounce of Prevention"