Heater Control with Automation - Further Reading

Heater Control with Automation

A pool heater can operate using its own control panel or it can be controlled by an Automation Control System. When a heater is controlled by automation the heaters temperature control is usually set to the maximum temperature and the automation control the heater operation to maintain its water temperature set point.

Some pool heaters indicate on its display panel when it is being controlled by automation. Other heaters show no indication of automation control on the heater display.

There are two types of connections that can be used between a heater and automation - "fireman's switch" control or RS485 data connection. The use of the fireman's switch is the standard way most heaters are controlled by automation.

2 Wire Fireman's Switch Control

Every pool heater, both gas and heat pump, has a "fireman's switch" 2 wire low voltage (24V) control circuit, and every automation system has a connection for heater control of a "fireman's switch". That means you can use any manufacturers heater with any automation system.

The "Fireman's Switch" is a poor name for the 2 wire 24 volt simple remote connection in the heaters safety circuit that controls turning the heater on or off.

The fireman's switch circuit is low voltage, supplied by the heater. You do not connect the 2 wire fireman's switch to 120 volts. The high voltage power and low voltage "fireman's switch" should be run in separate conduits between the heater and the automation load center. Although some pool companies will run the fireman's switch wire through the same conduit with the high voltage wire it isn't recommended and not to most recent NEC code. The heater should be wired to always be powered on and set at max temperature.

The automation system simply closes the fireman's switch circuit with a small relay on the main board to command the heater on and opens the fireman's switch circuit when it wants the heater off. It basically takes 24 VAC from the heater and sends it up one wire, through the Fireman's switch relay on the automation board and then back to the heater. When this loop is closed, the heater will run.

In some heaters, like the Pentair MasterTemp, the heater control panel looks like the heater is off when the "fireman's switch" is open by the automation and the control panel only lights when the automation turns the heater on. In other heaters, like Raypak, there is an indication on the heater control panel when the automation is controlling the heater and has it off.

When using the "fireman's switch" the heater thermostat is not used. The automation system has it's own water temperature sensor that it uses for heater control. Sometimes the heater temperature and the automation water temperature do not agree. The automation water temperature controls the pool/spa temperature and the temperature displayed on the heater is for information and heater diagnostics only.

Automation systems usually have a water temperature sensor and an air temperature sensor. If the automation water temperature does not seem correct check that the water and air temperature sensors connections are not reversed on the automation board.

Raypak lets you override the Fireman's switch

The Raypak manual says: The digital heat pump pool heater can be easily controlled by most two-wire and three-wire remote systems. The digital display will flash “Remote” to let you know that it is under control of a third party automation system. Simply press the up and down arrows for 5 seconds to release the control from the remote mode and regain local control.

3 Wire Remote Control

Some heaters have a 3 wire remote control in addition to the 2 wire fireman’s switch. That gives use of separate pool and spa thermostat settings.

For a three wire remote, the heater sends 24 VAC out on the common wire and looks for it to return on the Pool terminal or the Spa terminal.

If it returns on the Pool terminal, that's the same as pressing the "Pool On" button.

If it returns on the Spa terminal, that's the same as pressing the "Spa On" button.

So, the heater is controlling the temperature based on whether the Pool On or the Spa On is selected.

When using a 3 wire setup, you move a jumper on the board to disable the "Pool On" and "Spa On" buttons on the heater membrane pad.

For a 3 wire setup, you have two remote switches. One for Pool On and one for Spa On. You can only close one at a time to select Pool or Spa.

RS485 Heater Control

Some heaters have a digital 2, 3 or 4 wire control circuit that can allows the automation system from the same manufacturer to control the heater. RS485 control is more often used in Heat Pumps that can run in both heat or chiller modes. Using the RS485 connection can display more information and give more controls depending on the automation system.

Some automation panels require specific firmware levels to connect to a heater via RS485.

In general using the "fireman's switch" is the preferred simple method of heater control unless you require some automation features that only come with the RS485 controls.

Timer Control

If a pool does not have an automation system the heater "fireman's switch" may be connected and controlled by the same timer as the pool pump. Gas heaters should be turned off to cool down about 20 minutes before the pool pump stops water flow through the heater.

Intermatic has the 156T4042A Fireman Switch that comes on select timers or can be purchased separately to add to its mechanical timers. The 156T4042A Fireman Switch provides coordinated control for any pool/spa heater and filter pump. It is designed to turn OFF a gas fired pool/spa heater approximately 20 minutes before the filter pump shuts down. This eliminates the problem of pounding and knocking caused by overheated water and also reduces scale and lime deposits and extends service life of the heater.