I explain based on the Example File: HeatRecoveryElectricChiller.idf. Please find the revised idf file Here. It's EnergyPlus V9-6-0.

What I revised are as follows:

1. WaterHeater:Mixed has been replaced by HeatExchanger:FluidToFluid.
2. In PlantLoop, Plant Side and Demand Side of Heat Recovery Water Loop have has been swapped.replaced.
3. Sizing:Plant objects have has been added.

Only the first revision is not sufficient. You have the severe error. Drawing a water-side schematic helps to identify the cause.

HeatExchanger:FluidToFluid needs to be connected to two Loops, and one should be Supply Side and the other should be Demand Side. However, both sides of WaterHeater:Mixed in HeatRecoveryElectricChiller.idf are Supply Side. For the second revision, you can swap Node, Branch List and Connector List Names of Plant Side (Supply Side) and Demand Side as follows.

Third revision is required if some parameters of HeatExchanger:FluidToFluid are "autosize". In my revised idf file, I have set Heat Exchanger U-factor Times Area Value to "autosize".

I explain based on the Example File: HeatRecoveryElectricChiller.idf. Please find the revised idf file Here. It's EnergyPlus V9-6-0.

What I revised are as follows:

1. WaterHeater:Mixed has been replaced by HeatExchanger:FluidToFluid.
2. In PlantLoop, Plant Side and Demand Side of Heat Recovery Water Loop has been replaced.
3. Sizing:Plant objects has been added.

Only the first revision is not sufficient. You have the severe error. Drawing a water-side schematic helps to identify the cause.

HeatExchanger:FluidToFluid needs to be connected to two Loops, and one should be Supply Side and the other should be Demand Side. However, both sides of WaterHeater:Mixed in HeatRecoveryElectricChiller.idf are Supply Side. For the second revision, you can swap Node, Branch List and Connector List Names of Plant Side (Supply Side) and Demand Side as follows.

Third revision is required if some parameters of HeatExchanger:FluidToFluid are "autosize". In my revised idf file, I have set Heat Exchanger U-factor Times Area Value to "autosize".