Zone Valves and Hot Water Heating Systems

By Mark J. Donovan

Do you have a hot water heating system? If so, have you ever wondered what those small metal boxes hanging off of your hot water piping near the boiler are? Well they are zone valves and they play an important role in your hot water heating system.

A hydronic zone valve, as it is officially is called is the mechanism in your hot water heating system that allows hot water to flow from the furnace to your zone heating elements. It is powered by a local 24V AC power supply that is usually located near the boiler.

A zone valve works in conjunction with your home’s boiler, circulator pump, and thermostat. When the thermostat sends a low voltage signal to your furnace to supply hot water to the baseboard heating elements it is actually sending a signal to the zone valve and the circulator pump. It is telling the zone valve to open up and allow hot water to flow through the heating elements. The circulating pump acts to circulate the hot water generated by the furnace, through the closed hot water heating system.

When the thermostat indicates that the particular room or heating zone is warm enough it then sends a signal back to the zone valve to turn off.

Frequently you will see multiple zone valves installed in a hot water heating system. What this means is that there are multiple heating zones within the home that are controlled by different thermostats, and thus the reason for multiple zone valves.

Sometimes a zone valve can fail and stay in a stuck on position. When this situation occurs the room, or zone, will continuously be heated. Other times the zone valve could fail to the stuck-on position. When this occurs, no hot water will flow through the heating elements. In either case a plumber should be called.

So that’s what those little metal boxes hanging off of your boiler’s piping system are all about.