Combustion Lockouts on Heatmaker H/HW Plus & Mark II Units
Heatmaker is committed to providing you with information that can help you avoid mechanical malfunction before it becomes an issue. This describes lockout modes for the Heatmaker H/HW Plus units and for the Heatmaker Mark II units.
Lockouts are a critical safety feature that mitigates the possibility of a faulty start-up when the flame-sensing device fails to identify combustion within 5 to 7 seconds of gas valve opening or during the combustion cycle. The unit will attempt 3 cycles before going into lockout.
When the unit is in lockout mode, the internal pump will run continuously and its temperature, as seen on the temperature gauge, will drop below 160 degrees. The unit will reset by interrupting its power switch or a red 24-volt wire in control circuit.
There are three different failure modes leading to lockouts and, therefore, it is important to identify in seconds the length of time that the gas valve is powered. The length of the cycle will be either (a) 1 to 2 seconds, (b) 5 to 7 seconds, or (c) more than 10 seconds.
Failure Modes and Evaluation:
(a) 1–2 seconds. Power that is drawn by when the gas valve powers-on drops the 24 volts below the module’s minimum.
1. Many Mk-II units have a small tapered minimum pressure switch (2 red wires) which may leak causing it to ground out the 24-volt circuit. Remove two red wires and temporally jump to test operation.
2. Gas valve grounded or shorted: Read resistance across valve connections, with orange wire removed. Resistance should be 14 to 16 ohms.
(b) 5-7 seconds. The unit fails to identify strong flame signal.
1. Faulty Igniter. Read resistance across igniter, should be under 100 ohms(60-80 cold).
2. Confirm gas source is present either by observing that other commonly connected gas appliances are working or using water gauge at inlet of valve. (4” to 14” water column). [Do not attempt to measure gas pressure at valve outlet, as this is a negative pressure gas valve.]
(c) 10-plus seconds. The unit establishes flame but then fails after 10 seconds or longer.
This applies to concentric type venting (pipe 3” within a pipe 5” venting) through wall venting. Exhaust gases in the 3”inner pipe are leaking through connection joints into outer 5” air source pipe. These gases dilute air source and cause flame failure.
1. Typical identification is strong unpleasant smell at exhaust terminal.
2. Remove and repair (seal) the leaking joints) or replace venting with factory approved stainless vent piping.
If you have any questions, call Heatmaker’s technicians Monday-Friday, 5:00 a.m. – 7:00 p.m., EST; and Saturday 5:00 a.m. – 1:00 p.m., EST.
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