Hot water gets in the cold water line without running the pump.
In rare cases with some plumbing layouts, a large flow of cold water can create enough of a pressure difference to open the check valve, allowing some water flow through the pump from hot to cold. An example of this is when a fixture supplying the lawn sprinklers is on the outside wall where the Chilipepper is installed.
If you find hot water entering the cold line, you may need to increase the check valve spring force.
As can be seen in Fig 1 below, the valve is very simple. A rubber valve check is held against the opening in the pumping chamber that opens into the outlet tube by a spring. The spring is held in by the nylon retainer in the cold water outlet tube.
The normal position of the retainer is flush with the top of the outlet. To make the adjustment, insert the hex tool into the retainer and tighten 1/2 turn (clockwise) to increase the force of the spring on the valve check. Additional 1/2 turn adjustments can be made until the mixing problem is resolved. It is important to make these adjustments ONE AT A TIME and to check that the water flow is not being obstructed as that can cause damage to the pump.
Pump turns off but water isn’t hot. Have to push the button several times to get hot water.
If either of these issues are occurring then it is likely that the spring check valve is dirty. If any debris gets into the pump, it can get stuck in the check valve and keep it in the “open” position allowing the cold water to mix with the hot. A quick cleaning will get the unit working correctly again.
Cleaning the Check Valve
Referring to the figure below:
Remove the brass fitting from the cold water outlet of the pump.
Using the Hex tool included with the kit, remove the retainer from the outlet tube.
Remove the spring and the rubber valve check.
Wipe off the face of the rubber valve check with a cloth or sponge.
Look down into the outlet tube and check for any debris. Remove any debris with a Q-tip or something similar. *If it looks clean then it is clean enough.
Put the valve check and the spring back into the outlet tube with the valve check down.
Thread the keeper back into the outlet tube, leaving it flush with the top of the tube.
Thread the brass fitting back onto the outlet tube being careful not to over tighten it.
Be sure to purge the air from the pump before starting by following the priming instructions.