Most of our equipment uses Watlow PM temperature controllers. These controllers monitor temperatures through the thermocouples, and adjust an output signal to maintain the temperature at your set point. This output signal is a blower on most combustion systems, and a relay on most electric systems. The temperature controller also can trigger alarms based on temperature, and will shut down the equipment in case of an overtemp (high limit) situation.
Always take a picture of error codes, as the text shown is not always clear.
Error Codes
Interpreting the display, see below.
Common Error Codes:
Er. i1 Er.i2 – Input error. The thermocouple isn’t sending a signal to the controller. Input 1 is the process thermocouple (Temp shown on the home screen), Input 2 is the high limit thermocouple (only used for the high temperature cut-off).
This is usually cause by a loose connection or bad connection due to corrosion. Remove wires at the thermocouple head and check for corrosion. Remove and strip back to expose new wire if corroded. Clean out terminal with compressed air and small brush. Put wire back into termninal and tighten snug. Press reset on the controller, or cycle power.
The thermocouple may have also failed or broken. This can be ascertained by checking continuity with a multimeter. Check from the + to the – at the thermocouple head. If there is not continuity, the thermocuple has likely failed and will need replaced.
Controller not keeping set point
The temperature of the equipment not staying at the set point can be caused by several issues.
On gas equipment it can be caused by the gas/air tuning. Even at 0% the blower is still on a small amount to keep a flame. If the furnace is not cooling down quickly enough, you may need to decrease the gas at 0% to make the flame lean, which will cause the furnace to cool faster.
On electric equipment this can be a sign that a relay is stuck open or closed, and is not responding to the controller, or that an element has failed Change the controller to manual mode, and set the percentage to 0%. Wait 5 minutes, open the door and see if any elements are glowing red. If so, this means a relay is not opening when it should. Set the controller to 100%. Wait 5 minutes, open the door and see if any elements are not glowing. If one or more are not glowing, a relay could be stuck open or an element has broken.
If none of the above indicate an issue, it may be a problem in the programming of the controller. Older controllers had a setting called autotune (AUt.t) or truetune. Press the green advance button until you see AUt or ttUn on the screen and ensure it is set to off. If it has been set to on, turn it off. This setting automatically adjust many deeper settings in the controller and can often cause issues. If it has been turned on, you will need to reset controller settings to their default.
Buttons not working
Older controllers often have buttons that are hard to press or will stop pressing entirely. This is often caused by corrosion on the contacts that the buttons touch. By using a credit card and flat head screwdriver, the front plate of the controller can be pried off, and the back of the buttons and the gold contacts they press can be cleaned. Use alcohol to gently clean both. An eraser works well to rub off any corrosion.
If buttons stop working entirely and despite the above cleaning, you may need to have the controller refurbished. Contact Watlow for repair and refurbishment.
