Bypass Operation; Anti-Frost Heater Circuit - Rheem 874W27NF Service Manual

Sequence of Operation Component Diagram

BYPASS OPERATION

The bypass is a section of copper pipe work connected between the water body assembly
and the outlet of the heat exchanger and allows a quantity of cold water to bypass the heat
exchanger. The purpose of the bypass is to ensure the heat exchanger operates at
temperatures above the dew point of the combustion gases, ensuring condensate is not
produced, but low enough to maximise the heat exchanger life. The PCB activates the water
bypass control motor based on the heat exchanger temperature and the selected outlet
water temperature.

ANTI-FROST HEATER CIRCUIT

All models have an anti frost heater circuit. The anti-frost heaters are wired in series and
operate independently from the water heater.
A thermostat sensing ambient air temperature, positioned in the wiring loom near the bottom
of the water heater, activates the anti-frost heaters when the ambient air temperature falls to
4ºC +4ºC/-2ºC and deactivates the anti-frost heaters when the temperature rises above
12ºC.
In the event a heater block becomes open circuit the total heater circuit is rendered
inoperable. There are six anti-frost heaters in total.
Refer to „Anti-Frost Heaters‟ on page 55 for replacement procedure.
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TM061 Rheem 27 Water Star Service Instructions – Issued: 11/10
REV A Issued 08/13
Service. All printed copies not bearing this statement in RED are deemed "uncontrolled"
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