An error code 94 means the exhaust temperature is too high (condensing units). One of the benefits of installing a high efficiency tankless is the low exhaust temperatures that allow for the use of PVC, CPVC or PP venting (check local code to see if there are any additional restrictions).
A non-condensing tankless usually has exhaust temperatures above 300 degrees F and thus requires the use of category III stainless steel venting. A condensing unit uses a secondary heat exchanger to capture as much of that heat energy in the exhaust and put it into the water resulting is exhaust temperatures usually below 150 degrees F. As an additional safety measure our modern high efficiency tankless units have an exhaust temperature thermistor to monitors the temps and shut down the unit if they get too high.
Common Causes of the EC94:
- Scale build up. Excessive scale in the heat exchanger acts as an insulator and reduces the heat transfer into the water. This may also result in other overheat related error codes like the EC20 or EC14. A good indication of scale build up is the stainless steel heat exchanger surface starts to develop golden brown coloring on the surface.
- Restrictions in exhaust or intake venting. If the heater is unable to effectively pull in fresh air or remove the hot exhaust, the exhaust temps will rise. Make sure vent termination screens are clear of any debris or build up.
- Dirty fan. Similar to restrictions in the venting, if the fan has excessive build up, it will not be able to move as much air into or out of the unit.
On units that feature a display window, you might see an Error Code 941 or Error Code 942. These are both error codes related to exhaust temperatures being too high. Both error codes are warning codes when the detected exhaust temperature is over 167 degrees F, detecting EC941 three times will cause EC942 to be displayed and shut down the heater. Common causes above still apply to these 3 digit error codes.
For further technical assistance call 866-766-7489 or use our Contractor Locator to find a local service representative.