Here's what I found about the light blinking 4 times (Rheem Criterion II):
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4 Flashes
Pressure switch fails to close. When the blower is turned on, the control insures it that the vacuum switch is closed before continuing with the ignition sequence. If it cannot force the switch to close by cycling the blower, it will indicate this failure.
(The vacuum switch may also fail or fault during main burner. If this happens, then you will get a flash code of four.)
If blower motor is operating at speed and there are no vacuum restrictions, a closed pressure switch will allow 120V power to pass between the red (inbound) wire and the blue (outbound) wire.
Blocked venting will be a primary cause of this failure. If venting is blocked, then there is no power thru the vacuum safety switch to the control module and pilot valve.
Venting over-temperature switch will be another cause of this failure.
Check for rubber vacuum hose. Verify motor is running. Verify PVC venting is free and clear or all obstructions. Verify termination vent is free and clear of all obstructions. Verify venting does not contain an excessive number of elbows.
Verify 120V at the #8 (blue wire) on the control. If no power, verify 120V at the blue wire on the vacuum switch.
Verify vacuum safety switch is operating. Reset heater. Remove blue wire from
TECHNICAL SERVICE DEPARTMENT Technical Service Bulletin 1-800-432-8373
2 Inch PowerVent LED Indicator Explanations & Troubleshooting Table
Technical Competence, Product Confidence
Page 4 of 6
1610.DOC
LED Indicator Flash Explanation Reasoning Service Remedy vacuum switch and measure for 120V. If no 120V, then verify .75 inches w.c. with a magnahelic gauge. Replace vacuum switch.
Verify over-temp safety switch is not open (too hot). If 120V at the blue wire on the vacuum switch, but not at the #8 position of the control, then over-temp switch may be tripped. Cool switch to less than 1800.