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How to connect fireman switch to pool heater

Some Intermatic 24-hour mechanical timers have a fireman switch that comes pre-installed, or can be purchased separately.

The main function of the Intermatic timer is turning the pool pump on-off. The pump circulates water through the pool filter, and if the pool has a heater, the water also passes through the heater.
Timers with the fireman switch have added function and can turn off pool heater 20 minutes before pool pump.

You do not want the heater running when the pump is off.
But the heater does not require a timer with fireman switch. The heater has it's own control system and thermostat that operate completely independent of the Intermatic timer. The heater has a pressure switch that turns off automatically when water pressure in the water line drops. So when pump turns off, the water slows down, and heater turns off.

In addition to the pressure switch, the heater also has high limit switch that automatically turns off heater if water inside pipe is too hot. The limit switch gives heater a back up system if the pressure switch or thermostat fail.

However in some cases, you want the timer to turn off the heater before the pump turns off, so hot water is not left inside the pipe.
Purpose of fireman switch is to turn off heater 15-20 minutes before the pump.
That ensures maximum utilization of hot water, and ensures heater is not ON unless timer is ON.

The fireman switch provides additional layer of fail safe for the heater. And then both pump and heater work together to maximum efficiency and protection.

Note: The timer and heater are electrically separate.
They do not share same circuit breaker or control mechanism.
The timer is a simple motor-driven device like a clock. The heater has a circuit board that is controlled by thermostat and pressure switch.
The timer can be 120 volt and heater 240 volt, or reverse. It is not necessary for timer and heater to have same voltage.
There is only one common connection between the timer and the heater: using the fireman switch if heater has fireman's connection.

The fireman switch connection must be available on the heater, and looks like two small terminals, or two wires, inside a connection compartment on heater. The product manual will show if the heater has fireman switch connection.

Small 18 gauge thermostat-size wires are installed from the connection on the heater, over to the fireman switch on the timer.
The small wires carry 24 volt provided by the heater power supply.
These wires are NOT connected to 120-240 volt terminals on timer. The only thing the two small wires connect to are the fireman switch wires.
It is advisable to keep the small wires separated, and not touching the 120-240 volt wires that are present inside the timer wiring compartment. It is preferable if the two compartments were separated by a barrier, but this is not the case.

Basically the fireman switch is a simple on-off  SWITCH. When it is ON, it opens an override on the heater that lets the heater run. When it is OFF, then the heater is OFF.
What if heater does not have connections for fireman switch?
Not every heater has a fireman switch connection.

What if heater manufacturer says a fireman switch is not necessary? That means the manufacturer believes the pressure switch is reliable. It says they believe the cost of a bit of inefficient water heating is better than answering 1000s of questions from people wanting to know what a fireman switch is. Plus the omission of a fireman connection reduces complexity of manufacturing and cost of product.
After all we need less efficiency, cheaper products, and modular simplicity to meet public expectations.

How can a fireman switch be connected to the heater if there are no fireman switch connections?

You can look at manual and wiring schematic to determine if heater has connections for fireman switch.

For example the wiring schematic will show temperature limiter switches, and water pressure switch.

A good method for connecting fireman switch if no connections exist:
If you have access to the limit and pressure switch wires, then cut one of those wires .... that creates two ends ... connect each of those ends to the fireman's switch.

There is another way.
For example, most heaters have electronic ignition system that runs on 24 volt power from a transformer or power supply... usually there is junction box, or control access door. located on the heater where you connect 120 or 240V to the 24 volt power supply.

Cut one of the 24 volt wires and you have two ends. Connect those ends to fireman switch.

Interrupting power to the circuit board runs risk that control board will not complete the firing sequence, and could damage circuit board over time.... but I don't know this for fact.
fireman switch

Fireman switch

Buy:
156T4042A Fireman switch Amazon

Resources
Fireman's switch pdf
How to wire fireman's switch
Intermatic T104P201 timer

T104P201 Plastic box   24-hour 240V with fireman

pool timer in beige plastic indoor-outdoor  enclosure

T104R201  metal box   24-hour  240v with fireman

pool timer in beige metal indoor outdoor enclosure
24-hour timer
40 amp timer with Manual override supersedes programming until next programmed event.
Old style clock motor WG430
240Volt pool timer with fireman switch

Buy:
T104P201 plastic box at Amazon
T104R201 metal box at Amazon
156T1978 trippers at Amazon
156T4042A Fireman switch Amazon
Clock motor WG1573 at Amazon
Old style clock motor WG430
Resources:
T104P201 instruction manual
T104R201 instruction manual
How to set T100 series timers
How to wire fireman's switch
Intermatic T101R201
120Volt with fireman switch

Larger image

T101R201   metal box  120V with fireman switch

Beige metal indoor outdoor enclosure

T101P201   plastic box   120V  with fireman switch

Beige plastic indoor outdoor enclosure

120Volt pool timer with fireman switch
Buy:
T101P201 Plastic at amazon
T101R201 metal at Amazon
156T1978 trippers at Amazon
WG1570 Clock motor at Amazon
156T4042A Fireman switch Amazon
Clock motor WG433 at Amazon

Resources:
T101R201 manual
T101P201 manual
How to wire fireman's switch
Fireman's switch pdf
How to set and operate timer
Pool timer trippers and parts
How to troubleshoot timer
Wiring

Wiring diagrams: How to wire T104R3

Same as T014R
156T1961A tripper 156T1978 trippers Amazon
Can have 12 sets ON-OFF trippers on dial
WG1573 clock motor
Look for clock number

Clock motor can be replaced

Star screws
3 watt consumption = 26,280 watts per year = 26.28 Kwh per year @ .12 = $3.15 operating cost
60 Hz for US market/ 60 Hz for Europe Asia

Resource:
How to replace Intermatic clock motor

Adapt any timer above to different voltages:
Applies to T104, T174, WH40, pool timers etc
WG1573 for 60 Hz 208-277V  WG1573 208-240Volt at Amazon
WG1570 for 60 Hz 120V  WG1570 120Volt at Amazon
WG1576 for 60 Hz 480V WG1576 480Volt at Amazon
CW1570 for 60 Hz 24V
CW1570 24V at Aplus
WG1571 for 50 Hz 120Volt  WG1571 motor for 50 Hz 120Volt at Aplus
WG1574 for 50Hz 208-277V WG1574 motor for 50Hz 208-277V Amazon

Intermatic/ Grasslin enclosures

Metal and plastic enclosures
Intermatic enclosures

Intermatic sprinkler timers and wiring

Intermatic sprinkler timers
How to wire Sprinkler timers + rain sensor + manuals + buying options
How to connect rain sensor when timer does not have rain terminals
How to Set & Troubleshoot Intermatic sprinkler timer/ pdf

Multi-function timers and wiring 40 amp

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T1906-5  T1975-6 heavy duty timers 20 amp

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ET series digital timers/ 20-30 amp/ 120-277 volt/ multi-channel (same timer controls two circuits with different programming)

ET series timers
          Intermatic ET279 timer    Et70215 timer

Timer modules/ 16 amp/ 12-240 volt

Timer modules/ 16 amp/ 12 to 240 volt
MIL72E timer    FM1-timer   MIL72A timer      CN101A timer wiring        Intermatic PB300       

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