Error codes and replacing parts

Customer: "My heater is displaying an EO5 error code. Can you tell me what the problem is and how much it will cost to repair?"

TPR: I can't tell you what is wrong until I come out and troubleshoot it. 

Customer: "I looked it up. It is a stack flue sensor. How much for that? 

TPR: I can tell  you the price to replace that part, but there is no guarantee that that will fix the problem.

Explanation

The above exchange happens often. Error codes do not tell what the problem is. They point in a general direction. Most "do it yourselfers" and many inexperienced pool guys assume that an error code tells you what sensor to replace. It isn't that simple. One should always start with the possibility that the sensor is doing its job--that it is working correctly--and is telling you something about the heater. 

So, with the above example, a stack flue error isn't necessarily telling you that the sensor is bad. It may be that the temperature at the exhaust (the stack flue) is excessive. If you get this error a prudent and careful tech will need to rule out this possibility before replacing the sensor. 

This is why troubleshooting matters. 

What would cause excessive exhaust temperature? 

• poor water flow through the heater could cause this
• incorrect adjustment of the gas valve
• excessive soot build up on the heat exchanger
• a blockage in the vent (more likely with indoor installations)

Now, it could be a bad sensor, but that is not the starting point. Sensors aren't put in a heater to simply be replaced. They are part of the design because they can point to underlying problems.