Multiple heating zone control for hydronic (hot water) heating systems by using multiple zone circulator pumps and relays.s?

Page top photo: three hot water or hydronic heating zones, each served by an individual Taco circulator pump (visible in the photo) and individual zone circulator relay control (not in the photo).

This article series describes how to diagnose & fix circulator pump problems on hot water or hydronic heating systems.

How do we control hot water flow when using multiple circulator pumps?

Heating circulator pumps or "zone circulators" are used to force hot water from the heating boiler through radianting devices such as hot water baseboards or radiators.

The circulator is switched on as needed or in some designs may be wired to run continuously.

Here we discuss the wiring details when using multiple circulator pumps, one for each heating zone.

Each circulator zone is controlled by its own room thermostat. The thermostat in turn operates a circulator relay that turns on or off the circulator pump in response to a call for heat. The first circulator may be controlled by a relay in the heating boiler's primary control.

Additional circulators are controlled by individual circulator relays that are switched on or off by the thermostat.

We explain in more detail at MULTIPLE HEATING ZONE CONTROL that some heating contractors prefer using individual circulator pumps, one per zone, perhaps because they recall the history of unreliable zone valves which tended to clog or jam in some models by some manufacturers.

Others prefer to use one circulator pump and to control individual hot water heating zones by zone valves.

 

Circulator Pump Wiring Connections for Multiple Circulators

When a building uses multiple circulator pumps to control two or more heating zones (or one heating zone and a separate "zone" to heat an indirect fired water heater) then typically

1. The first circulator is controlled by the C1 and C2 terminals in the primary heating boiler aquastat while
2. Additional zones are controlled by additional circluator switching relays.

Note: If your building uses only one circulator pump but has multiple heating zones, you're probably using zone valves.

If that's your case see ZONE VALVES, HEATING - home or see our ZONE VALVE MANUALS & WIRING INDEX

Typical Wiring for Multiple Circulator Pumps controlling Multiple Heating Zones

If we wire each of multiple thermostats to an individual circulator relay switch that in turn will control the circulator for that heating zone. The low voltage thermostat controls the line-voltage powered circulator through its individual circulator relay switch.

The multiple zone circulator wiring diagrams below are excerpted from this manual: HONEYWELL R845A SWITCHING RELAY FOR HEATING ZONE CONTROL [PDF]

Wiring for the First Circulator of a Multi-Circulator Heating Zone System

Above we see that the first circulator powereed through connections to terminals C1 and C2 in the primary aquastat - in this example an R8184 or L8184 or similar control.

The room thermostat for this first zone - we'll call it "zone 1" connects to the T1 T2 terminals in the primary aquastat.

Wiring for Additional Zone Circulators after the First

For additional heating zones controlled by thermostats, zone relays, and individual zone circulator pumps, the room thermostat connects to an individual circulator relay and on a call for heat, activates that relay (closes it) so that the relay then provides line voltage to the individual circulator pump.

For examples of circulator relays and more wiring examples, see

• CIRCULATOR PUMP MANUALS

and these example IO Manuals for circulator switching relays:

• HONEYWELL R845A SWITCHING RELAY FOR HEATING ZONE CONTROL [PDF]
• HONEYWELL Tradeline RA 116A-RA117A-RA817A_MANUAL [PDF] - illustrated below
  
  Excerpt: The R845A Switching Relay provides DPST switching for hydronic zone controlled heating systems or SPST conrol of two separate loads. One load must be line voltage. The other may be line or low voltage.
  
  The R845A may be directly cntrolled by any 2-wire series 80 thermostat,such as the T86A (Honeywell) ...
  
  Terminals 3 and 5 are not connected to an internal power source. Connections [to use these] must be made to the R845A power supply or to a separate power supply.

Below is a generic wiring diagram included in many B&G circulator pump manuals. It simply tells us that each individual circulator pump is wired through a separate control relay. We've edited the drawing for clarity and detail.

 

- See BELL & GOSSETT B&G EQUIPMENT MANUALS & CONTACT for our complete collection of B&G circulator manuals

See CIRCULATOR PUMP MANUALS to find the wiring diagram for your specific heating zone circulator pump.

Below we include another Multi-Circulator Heating Zone Wiring Control example from Taco,

Above excerpted from

• TACO SR503-4 SWITCHING RELAY INSTALLATION INSTRUCTIONS [PDF] (2010) and wiring diagrams
  Excerpt:
  When any thermostat calls for heat, the appropriate circulator is energized and the isolated end switch (X and X) will start the boiler.

More Taco zone controls are at

• TACO DIAGRAMS, MANUALS, PARTS, CONTACT

Priority Zone Circulator Wiring Example

A similar example wiring diagram below provides a contrast: showing multiple priority circulators using zone valves.

The zone valve is controlled by a circulator; each circulator end switch in turn switches on the circulator in response to a call for heat.

How do we make sure hot water only enters the zone calling for heat?

Our reader asked:

When using multiple circulator pumps for zoning, what stops the water from enterning the other zones? (July 3, 2012) Anonymous

Reply: the flow control valve

Anon: the flow-control valve, a check valve usually found at the boiler hot water riser pipe(s), prevents water from circulating through zone piping until the circulator for that zone begins to spin - causing a more significant pressure difference across the zone.

That check valve also prevents hot water from circulating into a zone by natural convection when the thermostat is not calling for heat.

See CHECK VALVES, HEATING SYSTEM for details about flow control valves.

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Reader Q&A - also see RECOMMENDED ARTICLES & FAQs

Where can I find a control panel for a two-boiler heating system with multiple circulators?

Is there a control panel for a two boiler furnace with 3 zones with pumps? On 2022-04-26 by John

by Inspectapedia Com Moderator (mod)

@John,

A "furnace" in my lexicon is a hot air heating system.
A "boiler" heats water - such as forced hot water radiators, baseboards, or maybe a steam boiler and steam radiators.

A "two boiler" heating system might be referring to what's called a "cascade" arrangement. The control that responds to the thermostat turns on boiler #1 and if the heat output is not sufficient, or if temperatures are low-enough, then might turn on boiler #2 in addition.

So sure, there are cascade boiler control systems - if that's what we're discussing.

And on this page we discuss wiring for multiple-circulator systems to support multiple heating zones.

...

Continue reading at CIRCULATOR PUMP MANUALS for individual circulator pump wiring diagrams, or select a topic from the closely-related articles below, or see the complete ARTICLE INDEX.

Or see these

Recommended Articles

• CIRCULATOR PUMP MANUALS
• CIRCULATOR PUMPS & RELAYS - home
• CIRCULATOR PUMP RELAYS & OTHER CONTROLS  - using circulator pump relays to control hot water heat zones
• CIRCULATOR PUMPS vs ZONE VALVES
• MANUALS & PARTS GUIDES - HVAC - home
• MULTIPLE HEATING ZONE CONTROL - using multiple circulators to control hot water heat zones
• ZONE VALVES, HEATING - home
• ZONE DAMPERS - warm air heating system zone control.

Suggested citation for this web page

MULTIPLE CIRCULATORS HOW TO HOOK UP at InspectApedia.com - online encyclopedia of building & environmental inspection, testing, diagnosis, repair, & problem prevention advice.

Or see this

INDEX to RELATED ARTICLES: ARTICLE INDEX to HEATING BOILERS

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