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AFUE DEFINITION, RATINGS
AGE of CHIMNEYS & FIREPLACES
AGE of AIR CONDITIONERS & HEAT PUMPS
AGE of HEATERS, BOILERS, FURNACES
AGE of WATER HEATERS
AIR CONDITIONING & HEAT PUMP SYSTEMS
AIR FILTERS for HVAC SYSTEMS
AIR FLOW MEASUREMENT CFM
AIR HANDLER / BLOWER UNITS
AIRBOUND HEAT SYSTEM REPAIRS
ANTIFREEZE for BOILERS
ANTI SCALD VALVES
APPLIANCE EFFICIENCY RATINGS
BACKDRAFTING HEATING EQUIPMENT
BACKFLOW PREVENTER VALVE, HEATING SYS
BACKFLOW PREVENTER, HEATER WATER FEEDER
BACKUP HEAT for HEAT PUMPS
BANGING HEATING PIPES RADIATORS
BLOWER FAN CONTINUOUS OPERATION
BLOWER FAN OPERATION & TESTING
BLUE vs YELLOW COMBUSTION FLAMES
BOILER LEAKS CORROSION STAINS
BOILER NOISE SMOKE ODORS
BOILER OPERATING PROBLEMS
BOILER PRESSURE & TEMPERATURE SETTINGS
BOOKSTORE - InspectAPedia
BTU USAGE MONITORS
CAPACITORS for HARD STARTING MOTORS
CARBON MONOXIDE - CO
CHIMNEYS & Flues - Asbestos Transite Pipe
CIRCULATOR PUMPS & RELAYS
COOL OFF HEAT, Thermostat Switch
COMBUSTION PRODUCTS & IAQ
COMPLETE COMBUSTION, Stoichiometric
CONVECTOR HEATERS - HYDRONIC COILS
CREOSOTE FIRE HAZARDS
DEFINITION of Heating & Cooling Terms
DIAGNOSE & FIX AIR CONDITIONER / HEAT PUMP
DIAGNOSE & FIX HEATING PROBLEMS-BOILER
DIAGNOSE & FIX HEATING PROBLEMS-FURNACE
DIRECT VENTS / SIDE WALL VENTS
DRAFT HOODS - gas fired
DRAFT MEASUREMENT, CHIMNEYS & FLUES
DRAFT REGULATORS, DAMPERS, BOOSTERS
DUCT SYSTEM & DUCT DEFECTS
ELECTRIC HEAT, DIAGNOSIS, REPAIR
ELECTRIC MOTOR DIAGNOSTIC GUIDE
ELECTRIC MOTOR OVERLOAD RESET SWITCH
ELECTRICAL POWER SWITCH FOR HEAT
FAN, AIR HANDLER BLOWER UNIT
FAN AUTO ON Thermostat Switch
FAN CONVECTOR HEATERS - HYDRONIC COILS
FAN LIMIT SWITCH
FILTERS, AIR for HVAC SYSTEMS
FILTERS, OIL on HEATING EQUIPMENT
FIRE SAFETY CONTROLS
FIREPLACES & HEARTHS
FLAME COLOR, BLUE vs YELLOW COMBUSTION
FLOODED HEATING EQUIPMENT REPAIR
FLUE SIZE SPECIFICATIONS
FLUE VENT CONNECTORS
FREEZE-PROOF A BUILDING
FUEL OIL TYPES & CHARACTERISTICS
FUEL UNIT, HEATING OIL PUMPS
FURNACE CONTROLS & SWITCHES
FURNACE EFFICIENCY, HIGH vs MID
FURNACE HEAT EXCHANGER LEAKS
FURNACE OPERATION DETAILS
FURNACE OPERATING TEMPERATURES
GALVANIC SCALE & METAL CORROSION
GAS BURNER Flame & Noise Defects
GAS FIRED WATER HEATERS
GAS PIPING, VALVES, CONTROLS
GAUGES ON HEATING EQUIPMENT
GEOTHERMAL HEATING SYSTEMS
HEAT EXCHANGER LEAKS
HEAT LOSS INDICATORS
HEAT LOSS PREVENTION PRIORITIES
HEAT PUMPS, DIAGNOSIS, REPAIR
HEATING COST FUEL & BTU Cost Table
HEATING COST SAVINGS METHODS
HEATING OIL PIPING TROUBLES
HEATING OIL TANKS
HEATING OIL TYPES & PROPERTIES
HEATING SMALL LOADS
HEATING SYSTEM INSPECT DIAGNOSE REPAIR
HEATING SYSTEM NOISES
HEATING SYSTEM SERVICE & MAINTENANCE
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HIGH EFFICIENCY BOILERS/FURNACES
HOT WATER HEATERS
LP & Natural Gas Safety Hazards
MANUALS & PARTS GUIDES - HVAC
MIXING / ANTI-SCALD VALVES
MOTOR OVERLOAD RESET SWITCH
Natural Gas Combustion
NO HEAT - BOILER
NO HEAT - FURNACE
NOISE AIR CONDITIONER / HEAT PUMP
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NOISE, HEATING SYSTEMS
ODORS & SMELLS DIAGNOSIS & CURE
ODORS in AIR HANDLERS & DUCT WORK
ODORS FROM HEATING SYSTEMS
OIL BURNER SOOT & PUFFBACKS
OIL FILTERS on HEATING EQUIPMENT
OIL LINE CLOGGING FIX
OIL LINE QUICK STOP VALVES
OIL LINE SAFETY VALVES
OIL ODORS, LEAKY OIL TANK PIPING
OIL PUMP FUEL UNIT
OIL SPILL CLEANUP / PREVENTION
PLASTIC HEATER VENT
PULSE COMBUSTION HEATERS
PRESSURE REDUCING VALVES
PUFFBACKS, OIL BURNER
PUMPS, PONY PUMPS
RADIANT HEAT TEMPERATURES
RELIEF VALVE LEAKS
RELIEF VALVES - TP Valves on Boilers
RELIEF VALVES - STEAM TP VALVES
RELIEF VALVES - Water Heaters
RELIEF VALVES - Water Tanks
Reset Switch - Heater Primary Control
Reset Switch Broken - Quick RepaiR
RESET SWITCH - ELECTRIC MOTOR
Reset Switch - Stack Relays
SAFETY, HEATING INSPECTION
SAFETY RECALLS, Chimneys, Vents, Heaters
SOLAR HEATING SYSTEM DESIGNS
SOOT on OIL FIRED HEATING EQUIPMENT
SPILL SWITCHES - Flue Gas Detection
SPLIT SYSTEM AIR CONDITIONERS & HEAT PUMPS
STACK RELAY SWITCHES
STEAM HEATING SYSTEMS
Thermal Expansion Cracking of Brick
THERMAL IMAGING, THERMOGRAPHY
THERMAL MASS in BUILDINGS
THERMAL TRACKING & HEAT LOSS
THERMOSTATS, HEATING / COOLING
THERMOSTATS, WATER HEATER
VIDEO GUIDES: Heating System Videos
WATER HEATER SAFETY
WATER HEATERS for HOME HEATING USE?
WINTERIZE A BUILDING
WOOD, COAL STOVES & FIREPLACES
WOOD STOVE SAFETY
Zone valves on hot water heating systems: what is a zone valve, how do they work, and how do I troubleshoot, install, repair or replace a zone valve? This website answers most questions about Heating System Boiler Controls on central heating systems to aid in troubleshooting, inspection, diagnosis, and repairs. The photo above shows a a bank of six zone valves controlling heat distribution in a large home.
Green links show where you are. © Copyright 2013 InspectAPedia.com, All Rights Reserved. Author Daniel Friedman.
While going through the detailed sequence in the operation of the heating boiler, watch for and inspect the condition of the heating boiler controls and safety devices (as required by ASHI 9.1.A.3 automatic safety controls).
A typical design will include a thermostat on the water heater that will cause hot water from a physically separate heating boiler to circulate through the heating coil located in the bottom of the indirect-fired water heater.
A separate loop of piping conducts water from a nearby heating boiler, through the coil in the bottom of the indirect fired water heater tank (thus transferring heat to water in the water heater tank), and back to the heating boiler.
Sketch (left) courtesy of Carson Dunlop Associates.
The water temperature inside the indirect fired water heater tank is sensed by a thermostatic control that causes the hot water tank's contents to be re-heated as needed, typically by turning on a circulator pump that moves hot water from the separate heating boiler through the coil in the bottom of the water heater.
While typical indirect water heaters use a heating loop encompassing a circulator pump and check valve, some systems may use a zone valve in this piping loop that first opens to let hot water flow though the piping loop (boiler to water heater coil and back to boiler), and second, when the valve has opened, it turns on a circulator pump to cause water movement.
This arrangement (or a simple check valve) prevents water in the hot water tank from being heated by the boiler when it is not needed (circulating by convection, for example).
See Indirect-fired Water Heaters for details.
Frequently Asked Questions (FAQs) About Zone Valve Controls for hot water heating systems
Question: After adding a third zone valve one of my other heating zones stopped working
I have a two zone heating system with two thermostats and one circulator. I recently added a third zone for my basement. I have not wired in the zone valve and T-stat yet for the new zone. Since adding my third (non active) zone my 2nd floor zone has stopped working. If I manually open the valve then when the circulator starts to heat the first floor it pushes water around the second floor as well. I have tried testing voltages across terminals 1 and 2 and 2 and 3 but I get no readings either on the bad zone or the good one. I would have expected to see 24V on at least the working zone but I don't. Why is that ?
It wound up being an airlock. I just kept purging and purging and eventually got it.
Will, when you added the new zone valve to the heating system piping, the operation of cutting the heat distribution piping and soldering in the new zone valve could have introduced air into the heating system. If you didn't bleed that air out or provide an automatic air bleeder in a location that would do that for you, your system could be airbound. To check for, diagnose, and fix that problem, see AIRBOUND HEAT SYSTEM REPAIRS if you need to address this problem again.
Question: zone valve makes clicking noise when it is fully open and gear motor continues to run
Eric zone valve vt2343g13a02a works good but when in the open position it keeps clicking like the gear motor continues to run and the gear is clicking on the last tooth of the actuator or something???? - Ken 11/23/11
Ken a zone valve that keeps clicking suggests to me that either
the zone valve motor gears have become stripped or
the valve assembly is jammed and is not opening fully - the motor is unable to turn the valve to the fully open position, it is not reaching its "end switch" position, so it keeps trying to open the valve. Most likely you need to replace the unit.
Question: upstairs heating zone won't turn on or doesn't receive heat
My upstairs heating zone is not turning on this year. I have checked the setting on the Electronic Aquastat L 7124/L7148 and can not find anything amiss. What might I be missing? - Lisa 12/30/11
See AIRBOUND HEAT SYSTEM REPAIRS
Question: two zone boiler, single circulator pump replaced, now one zone doesn't heat
I have a two zone boiler with a single circulator pump that was recently replaced. I'm now having trouble with ciculation for one of my zones. I think its the zone valve itself though when the thermostat calls for heat I see the valve adjust and I can also set the arm into manual. My question is, is there a way test further if the valve is faulty. My instincts say if I can set the valve and it responds to the thermostat then its not faulty. Thanks - Chris 2/12/12
Chris, as the circulator pump is running (else your working zone would also be cold) I suspect that either the zone valve is stuck shut or that zone is air bound. You are right that setting the room thermostat up above room temperature should cause the valve to open, but if the zone valve itself is jammed or if the zone is air bound you won't get heat.
Question: Taco zone control valves 571, 573 led to short heating cycles
I Installed two Taco zone controls 571 & 573, and now I have short heating on cycles. I never had this problem before, for 47 years. I had to replace the zone controls because the old zone valves started to stick, but they were not Taco brand. I replace the thermostat with a Honeywell TH3000 series, but that didn't solve the problem. - Anon
When the thermostat calls for heat the zone valve opens and the circulator starts pumping. It is the temperature of the water in the boiler that turns the burner on and off. By short cycling I presume you're meaning that the boiler stays on for just a short time, turns off, then quickly turns back on. Sometimes this is a normal event, for example when the first surge of cold water from zone 1 hits the boiler and turns it on, the boiler's burner may be able to heat up the boiler quickly and shut it off; the boiler would stay off for a while. But when zone 2 then opens and sends a new surge of cold water into the boiler it will start again quickly in response to that new temperature drop.
However, because it normally takes some time for the heating zones to actually satisfy the thermostat, once both zones are running your boiler should return to normal run times. If it doesn't I suspect a sensor or control problem at the boiler.
Question: boiler temperatures are too high and the circulator pump malfunctions
Our burner keeps getting hotter than 190 degrees and the circulator has been replaced six times in the last four months. Our aquastat has also been replaced. We had a double then a triple installed. The aquastat currently in place is an electronic hydrostat. The wiring to the burner has been replaced. What can be causing the Taco circulator to malfunction or the burner to get hotter than the settings on the aquastat? - Andrew D'Agostino 4/25/12
Andrew, 6 circulators in 4 months sounds quite odd and as if no one found the real problem. I have seen repeat curculator failures when the tech replaced just the motor or pump but left a bent or worn support that torqued against the shaft bearing and ruined the replacement. If course, limited to no onsite assessment i am not sure what's going on.
Question: Two zone valves on boiler, but one won't go on unless the other one is also on
I have 2 zone valves on my boiler and zone1 will not go on if zone2 is not on. When zone 2 is on everything works good.Is this a bad valve or a wiring issue. - Frank 10/8/2012
Frank, if you mean that the zone valve itself does not operate or it's end switch does not turn on the boiler unless another zone valve is on then it's likely to be a wiring problem. Watch out for the case of two different zone valve brands - sometimes their wiring hookup details are different.
Question: zone valve installation diagram
I need diagram for install zone valve - Manuel 10/8/12
Manuel, we don't know if you're asking about piping routing, zone valve location, or zone valve electrical hookup. The wiring for zone valves varies slightly among brands and models - and will be shown in several options on the instructions that came with your zone valve. As you are installing a valve, look in the box. I know, some fellows use the instructions to kneel on during work at the boiler, rather than reading materials. If you've lost the instructions, give us the zone valve brand and model and we (or you) can obtain the detailed instructions from the manufaacturer.
Typically there are four wires at the zone valve.
Two wires connect from the room thermostat to tell the zone valve to open or close in response to room temperature. They may be marked T1 and T2. Two other wires connect the zone valve end-switch (a switch that closes to make the circuit when the zone valve itself is fully open or shut) to the circulator relay. Those may be labelled C1 and C2.
Question: why should my bathroom heating zone always be calling for heat?
I am not sure if bathroom zone should always call for heat when no other zones ever call for heat unless I turn them up - Steve 10/12/12
Steve, Properly wired each zone normally calls for heat independently.
If your bathroom zone is always calling for heat, check for a short circuit in its thermostat wires, or for a defective thermostat, or a thermostat set higher than the room temperature.
Question: indirect fired water heater is making water that is too hot
We have an oil fired boiler situated on the ground floor which supplies heating to our radiators and also supplies hot water to our bathrooms and basins from a hot water tank situated in a cupboard on our landing. Recently the actuator to the hot water system seemed to fail as the water was becoming very hot irrespective of whether the hot water was on or off at the control panel situated by the boiler as long as the central heating was set at "on". I replaced the actuator to the hot water and it seemed to be ok for a while but then the problem recurred Can you advise please? The only thing I can think of is that recently our son in law opened all the valves to drain the hot water so that he could re-washer a hot tap. This may or not be relevant though. - Roger Cotton 10/28/2012
Question: 100 Series gas boiler is not heating all parts of the house
Have a 100 series gas boiler. Part of the house gets heat but part of the house isnt getting heat. Worked for about a week and stop working and cant figure out the problem. - Brand 11/4/12
Question: After service following flooding from Hurricane Sandy, our boiler keeps running almost constantly
After an annual maintenance visit I noted very hot water and the furnace running almost constantly. They replaced zone valves and charged me. I recently evacuated my house to avoid hurricane sandy. When I left I turned off oil burner and and turned off thermostat.
Zone Valve Issue:
Question: how do I wire one zone valve to cause another one to turn on?
How do you wire one zone valve to another. One controls the other? - Joe 11/22/2012
Question: Our opstairs zone makes noise as if it is opening, and the boiler turns on, but we don't get any heat
I have 2 zones to my furnace basement zone works , but the zone upstairs makes noices as if its working furnace kicks on (2 mins) but no hot water going thru pipes ... Help! - Terri 11/26/12
If your zone valve is actually opening and the circulator is running but the zone doesn't receive heat, it may be air bound. See AIRBOUND HEAT SYSTEM REPAIRS.
On the other hand, the zone valve motor may be making noises but the valve may be stuck and need replacement.
Questions & answers or comments about zone valves on hot water heating systems: installation, diagnosis, repair advice.
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