Zone Valve Not Working? How to Tell What Has Failed

Is the zone calling? Read the lights

Make it call. Turn that zone’s thermostat a few degrees above the room temperature. Resideo’s checkout for the V8043 starts the same way, by raising the zone thermostat above room temperature to make a call for heat.

Read the zone control’s lights. If a zone control box sits near the boiler, its lights show how far the call gets. On Taco’s ZVC403, green means power is connected, yellow means a thermostat is calling and its valve is powered, and red means the valve is fully open and has switched on the end switch relay. Argo’s AZ controls use green for a zone calling and red for a valve fully open, so read the labels on your own box.

No call light? The thermostat is not asking: see a thermostat not working. Taco asks whether the thermostat was changed lately, and says a current robbing thermostat on its heat motor valves needs a resistor across the valve’s terminals, or its program is lost the first time the valve runs. Taco’s Zone Sentry instructions say some power robbing thermostats need the resistor their maker supplies.

Call light on, no open light? The call reaches the valve and the valve is not finishing its stroke: checks 2 to 4.

Give it time, then feel the lever

Wait first. Caleffi says a heat motor valve, which opens by warming a wax capsule, usually needs two to three minutes to open fully, while valves driven by a small motor usually open in two to three seconds. Taco says a newly fitted Zone Sentry can take up to 35 seconds to charge before the valve turns, usually less after that, and its green light flashes while it charges.

The lever test on a Taco 570. Taco’s own test is to power the valve, wait 1 1/2 to 2 minutes, then pull down the manual lever. If it moves freely all the way, the valve is open. If it starts easy and then goes hard, the valve is not open. Taco’s full test has a technician read 24 volts and 20 to 23 ohms at the head first, and only then calls the operator, its power head, bad. Push the lever back up afterwards: Taco says that restores automatic operation.

Other makers. Caleffi says the lever on its Z-one travels through nearly all of the valve’s stroke, so it is a good indicator of the valve’s position. On a Zone Sentry, Taco says the override button carries a slot that shows where the valve is.

The Zone Sentry’s light. In Taco’s table, no light means the power is off, from no call or no power. A blink once a second is charging. A slow blink once every 5 seconds is too long a charge, with too little power from the transformer or too many valves on it as the possible causes, and a different thermostat among Taco’s fixes. A double blink is too long an opening, with something blocking the valve, dirt built up inside or a failed actuator as the possible causes. Taco’s reset is to remove the power for 5 seconds and restore it.

Open it by hand to get heat back

Honeywell Home V8043. Resideo says the valve can be opened with no power by moving the manual lever over the stop and pushing it slowly and firmly to MAN. OPEN, and it returns to automatic the next time it is powered. Its end switch, which turns on the circulator, is not switched on when the valve is opened by hand, so where that switch starts the circulator and boiler, that zone gets heat only while another zone has them running.

Caleffi Z-one. The other way round: Caleffi says the end switch in its 24 volt actuators is tripped when the lever is put in the manual open position.

Taco 570. Taco says push the lever in the power head all the way down to open the valve, and push it back up to restore automatic operation. Left down, it holds that zone open.

White-Rodgers and Erie. White-Rodgers says use its manual dial only in a power failure, or for testing the system before it is wired: turn it clockwise with your thumb until the word Open appears, and the valve returns to the thermostat when power comes back. Schneider Electric says the manual lever on its Erie VT and VS valves moves back to automatic the first time the valve runs electrically.

The power head, the transformer and the end switch

A failed head. Caleffi says most modern zone valves let a failed actuator be replaced quickly without removing the valve body or draining the system. Resideo says the whole V8043 powerhead can be replaced without taking the valve body out of the line, a damaged gear train means a new powerhead, and a burned out motor means a new motor. Taco covers the 570’s power head for three years from its date code and the body for five. White-Rodgers is different: it says drain the system before its valve head is unlatched.

The transformer. Low voltage zone valves take their power from a 24 volt transformer, and each maker gives how many one 40 VA transformer can run: three Taco 570s, four Honeywell Home V8043s, or twelve Zone Sentrys. A technician’s check on a 570, in Taco’s words, starts by reading for 24 volts at the head’s terminals to rule out a bad transformer, and its Zone Sentry fix for too little power is a larger transformer or a second one.

The end switch. Caleffi says a three wire zone valve’s end switch closes when the valve reaches fully open, and can start the circulator and the boiler. Resideo’s checkout expects the valve to open and the switch to make the circuit to the circulator at the end of the opening stroke. A valve that opens with no pump or boiler following it is one for a technician to trace.

A valve held open

Three reasons, from Taco. Taco says a 570 lets water through when unpowered if a pump upstream pushes more than the 50 feet of head it can hold back, if the manual lever has been pulled down, or if its surroundings make the operator’s piston stick.

Not every valve seals fully. White-Rodgers says its 1311 and 1361 valves are allowed a small leak when closed, up to two, four or six gallons an hour for its 3/4, 1 and 1 1/4 inch sizes at their rated pressure difference. Taco rates its Zone Sentry drop-tight.

Wear and dirt. Resideo says dissolved oxygen, found in systems often topped up with fresh water, makes the rubber plug inside the V8043 deteriorate and eventually fail, and Burnham’s MPO-IQ manual says a dirty system can seize zone valves. If the boiler needs topping up often, find out why: boiler pressure.

The full sort for a zone that stays hot, including hot water rising past a flow check valve, is in a radiator that won’t turn off.

Water at the valve, or a bang when it shuts

A drip. Resideo says a leaking V8043 means draining the system and checking whether the O-ring needs replacing, a job for a trained technician. Put a tray under it until then.

Rushing water or a bang. Resideo says its zone valves are designed for silent running in a properly designed and installed system, but water noise can come from too fast a flow, and piping noise from systems above 212 degrees with too little pressure. Weil-McLain’s WGO oil boiler manual recommends a pressure bypass valve on zone valve systems, to prevent too much flow in a single zone and water hammer when the valves close. More in a boiler making noise.