Faulty Controllers

Explanation:

Important: Always check preceding data sets, lockout could have occurred previously.

This data indicates that the thermostat (or aquastat) called for heat for 10 minutes (Version 3.0 and later: 5 minutes) and no power ever came out on the orange wire. Almost assuredly the cause is a faulty primary controller. However it could possibly be the result of chattering by the thermostat or aquastat. This is very unlikely, however, because even allowing for the time in the software loop, there should be repeated "THERMOSTAT ON"/"THERMOSTAT OFF" readings. To confirm, look at the previous data sets for indications of short cycling. Loose wiring is another possibility.

Explanation:

This data indicates chattering by the primary controller. The DETAILED RECORDING sequence does not start until voltage is sensed in the orange wire. (See Recording Sequence Chart, above) If the DETAILED RECORDING has started but your data shows erratic voltage readings, it is an indication of short cycling or chattering by the primary controller. In this case there is no indication of short cycling by the thermostat or aquastat.

If there had been short cycling by the thermostat, the data would show very short elapsed times between "THERMOSTAT ON" and "THERMOSTAT OFF" readings.

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Short-Cycling of Thermostat or Aquastat

With the OnWatch Model 41, burners that short-cycle because of problems with the thermostat or aquastat are very easy to diagnose. After completing the Data Analysis Sheet the data set will show something like the example below. In order to confirm the cause, using the [BACKWARD] key, examine and record data sets leading up to the lockout cycle. If the data resembles below, suspect short-cycling:

If you see several sets of rapid "THERMOSTAT ON" and "THERMOSTAT OFF" screens and the times lead right up to the last "THERMOSTAT ON", then it is almost assured to be short-cycling by either the thermostat or the aquastat. These short-cycles continue to lockout of the primary controller. This example assumes that as the building or water cooled down, eventually heat was being called for continuously. It is important to note that this may not always be the case. If the thermostat continues to short-cycle, the controller may go to lockout but the Model 41 will not detect this.

If the customer calls and says that the burner needs resetting but the OnWatch Model 41 does not display "FAULT DETECTED / CALL SERVICE COMPANY," it probably means the thermostat or aquastat is continuously short-cycling. It means that the controller had locked out but the thermostat or aquastat continued to cycle ON and OFF. In this case the very high set number will confirm the problem. It may be in the thousands.

 

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Fuel Supply Line Problems

Fuel problems can present themselves in many ways. There can be fuel supply line problems, slipping drive couplings, internal relief valve malfunctions, clogged nozzles, worn pumps, etc. We cannot address all of them, but we will look at what customers tell us are the most common.

Fuel Supply Line Problems

Very definitive diagnoses of fuel problems can be made with the OnWatch Model 41. In diagnosing any problem, the more data the better. If you have data from a vacuum sensor you will be that much further ahead. Record the data from the data set and think through the information.

This set shows that right from start-up there was high vacuum and low pressure. First, check previous data sets to determine what is "normal" for this burner. Higher than expected vacuum readings that are inconsistent indicate some kind of intermittent restriction on the supply side of the pump.

Another possibility is to have increasing vacuum. This generally indicates a partial restriction on the supply side. The pump is working, pulling fuel, but somewhere before the sensor there is a partial restriction.

A data set can show lower than expected vacuum readings with low pump pressure.

1. Is the operating line voltage reasonable? Low voltage will cause a motor to drag.
2. Importantly does it show that the motor is operating? Compare the "voltage jump up" of this data set with previous sets. Is it about the same? If it is then probably the motor is not binding. If the motor was binding there might be only one-half the usual voltage jump up.
3. This data could be caused by a pump that is worn and not pulling well, a partially slipping drive coupling, a relief valve that is sticking open, air getting into the supply line or some other reason.

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Diagnosing Motor Problems

Generally speaking, motors either run normally, have bad starting switches or have binding or locked rotors. Each condition presents itself very differently and each condition can be pinpointed.

Faulty Starting Switch

A motor with a faulty starting switch (often called a "dead spot") will show voltage readings that are very different from normal. [To see readings from a normal motor, see Part 1, above.]

When power is applied to the motor, the start windings are not engaged. As a result the motor draws only a few amps resulting in a minor voltage drop:

As shown above, the first voltage reading might be 116 volts. At the next snapshot, two seconds later, the voltage is still approximately the same. And at the next reading still the same. This will continue until the primary controller goes out on safety lockout. At that time the voltage will be OFF. As a confirmation, the fuel pressure will remain at zero because the pump is not turning.

Locked Rotor

A locked rotor or jammed pump will show its own classic signs. This time both the run windings and the start windings of the motor are engaged and remain engaged. There is a high amperage draw and therefore low voltage. Because the motor never gets up to speed, the start windings continue to draw heavily keeping the voltage low. Also you will notice that the voltage tends to creep up.

Since the introduction of fast lockout primary controllers, sometimes the controller will lockout before the thermal overload on the motor trips. This means that the only "red button" that needs resetting is on the controller. Unless you are there when the problem occurs, there is nothing to tell you that this is a motor problem. The OnWatch Model 41 can help you make the correct diagnosis.

Scenario "A" shows what might happen if the thermal overload trips before the controller while Scenario "B" is an example of data if the controller goes to lockout prior to the motor thermal tripping.

The most significant, telltale sign of a locked rotor is the voltage that creeps up before lockout while the pump pressure is zero. But also note that the fuel pump pressure readings remain at zero. The combination of no pump pressure with depressed voltage readings that creep up is a dead giveaway of a motor that is not turning.

Slipping Drive Couplings

A drive coupling between the motor and the pump that slips only occasionally can be a difficult problem to catch. If you were present when it slipped and you had a pressure gauge attached, you would see the problem and the cause would be obvious. Again, remember the basic rule of the Model 41: It simply records what you would record if you were there. This is an example of what the data might look like if a drive coupling slipped:

T-T ON/OFF & TIME	ELAPSED TIME	LINE VOLTAGE	STACK TEMP	UP/ DN	FUEL PRESS	FUEL VACU
T-T on 11:18:03	0:00	108	73	-	0	0
11:18:05	0:02	124	73	-	102	3
11:18:07	0:04	124	73	-	102	3
11:18:09	0:06	124	73	-	19	1
11:18:11	0:08	123	73	-	8	0
11:18:13	0:10	123	74	^	102	3

The data set shows that motor performance was okay and pump performance started out okay, but then pressure was lost AND vacuum went down. Because vacuum went down, it indicates that the pump was not drawing like it had been. You want to check for possible air leaks, but by looking at the data from this and previous sets, it will give you an indication of what is going on. You can be quite confident that this is not a pump or motor problem.

 

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Diagnosing CaD Cell Problems

Malfunctioning cadmium disulfide cells can be difficult to diagnose if the problem is intermittent. The cells or their circuits can fail during initial startup or later, just "out of the blue". The OnWatch Model 41 will provide supporting evidence to help close in on the problem. You will be able to know what was working and what was not working. The Model 41 will not necessarily point you directly at the CaD cell, but it will allow you to eliminate almost all of the other possible causes for the lockout.

CaD Cell Failures at Startup

If a CaD cell does not see flame at startup, you might see data like this. [NOTE: This was recorded on a furnace with a 45 second lockout controller.]

To analyze the data, start right from the beginning.

• Is the thermostat calling for heat? Yes.
• Is the thermostat chattering? No.
• Is the line voltage acceptable? Yes.
• Did the motor start? Yes.
• Was there fuel pressure? Yes.
• Was flame ever established? Yes.
  But this may be difficult to determine in certain circumstances. For example, if this had been on a boiler and the controller locks out in 15 seconds, there may not be sufficient time for the stack temperature to increase before the controller shuts down. Be sure to keep scrolling through all the data for any sign of a stack temperature increase.

This data set tells you that almost everything is working. The controller shut down because flame was never "seen" by either the CaD cell or the controller, or there was a problem with the CaD cell circuit wiring.