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AFUE DEFINITION, RATINGS
AGE of CHIMNEYS & FIREPLACES
AGE of AIR CONDITIONERS & HEAT PUMPS
AGE of HEATERS, BOILERS, FURNACES
AIR CONDITIONING & HEAT PUMP SYSTEMS
AIR FILTERS for HVAC SYSTEMS
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ANTIFREEZE for BOILERS
ANTI SCALD VALVES
APPLIANCE EFFICIENCY RATINGS
ASBESTOS IDENTIFICATION IN buildings
BACKDRAFTING HEATING EQUIPMENT
BACKFLOW PREVENTER VALVE, HEATING SYS
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BUILDING SAFETY HAZARDS GUIDE
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CHIMNEY INSPECTION DIAGNOSIS REPAIR
CHIMNEYS & Flues - Asbestos Transite Pipe
CHINESE DRYWALL HAZARDS
CIRCULATOR PUMPS & RELAYS
COOL OFF HEAT, Thermostat Switch
COMBUSTION AIR for TIGHT buildings
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CREOSOTE FIRE HAZARDS
Curved Brick Chimneys - Sulphation
CONDENSING BOILERS/FURNACES DAMAGE
CONVECTOR HEATERS - HYDRONIC COILS
DEFINITION of Heating & Cooling Terms
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DEW POINT CALCULATION for WALLS
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EVAPORATIVE COOLING SYSTEMS
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MANUALS & PARTS GUIDES - HVAC
METHANE GAS SOURCES
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MIX VALVE SCALD PROTECTION, Best Practices
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NO HEAT - BOILER
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RELIEF VALVE LEAKS
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Thermal Expansion Cracking of Brick
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TRANSITE PIPE CHIMNEYS & FLUES
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WATER HEATER SAFETY
WATER HEATERS for HOME HEATING USE?
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WATER SOFTENERS & CONDITIONERS
WINTERIZE A BUILDING
WOOD, COAL STOVES & FIREPLACES
WOOD STOVE SAFETY
This article explains types of check valves used on hot water heating systems. Here we explain heating boiler check valves, also referred to as flow control valves, flo-control valves: controls that prevent hot water from circulating in the heating system when it is not supposed-to. We also discuss IFC circulators - internal flow control circulators, and heating system backflow preventer valves. This website answers most questions about Heating System Boiler Controls on central heating systems to aid in troubleshooting, inspection, diagnosis, and repairs. If you are looking for information on water supply piping & well system check valves see WATER SUPPLY SYSTEM CHECK VALVES.
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Check Valves on Hot Water Hydronic Heating Systems - Flow Control, Flo-Control Valves, Inspection, Settings, Problems
For an example of how the check valve or flo-control valve functions on hot water heating systems, and what goes wrong, also see Heat Won't Turn Off - Stop Unwanted Heat. Contact us to suggest text changes and additions and, if you wish, to receive online listing and credit for that contribution.
Check valves on heating boilers prevent hot water from circulating through the building when it is not supposed to be doing so - such as when the boiler and its water are still hot but the thermostat has stopped calling for heat.
Why Are the Baseboards or Radiators Hot Even Though the Thermostat is Set Lower than Room Temperature? Un-wanted Gravity or Convection Circulation of Hot Water
If electrical power switch to a hot water heating boiler is in the on position (see ELECTRICAL POWER SWITCH FOR HEAT) and the room thermostat is set below the current room temperature, the heating system (hot water or steam) boiler or (warm air) furnace should not run.
But for hot water heating systems (baseboards, radiators), other defects could cause or permit hot water to circulate through the heating system by "gravity" (convection, warm water rising on its own through the heating piping) even though the thermostat is not calling for heat.
[Warm water is less dense than cold water and will rise up through cooler water, displacing it and sending cooler water down to the boiler.]
The problem, if this is occurring, is usually that a check valve (photo above-left) (found internal to some circulator pumps, or external as a physical device) intended to prevent hot water from circulating on its own - when the circulator pump is off - is either set to a "forced open" position, or it has become defective (less likely).
If that's the problem (diagnosed by a heating and service technician) then the valve or circulator needs to be replaced. While waiting for that repair to be made, you can still turn off the heat when it is not needed, by turning off electrical power to the boiler. With the heating boiler switched off it will cool down and water will stop heating the radiators by gravity or convection circulation.
The red Bell & Gossett B&G flo-control valves shown in our photo above and in the sketch at left are designed to prevent hot water from circulating in a heating system unless the circulator pump is also running.
The valve provides a vertical-lift check valve function: until the circulator pump begins to run, the valve will prevent hot water from circulating through the piping system.
The B&G installation sketch (left, edited) shows a simplified but typical location of a flo-control valve - the red device at the right-most side of the sketch.
Which way do we turn the lever on a flo-control valve?
The lever on the top of the B&B flow control valves shown here allows the user or service technician to force the valve to an "open" position, overriding the valve's automatic internal operation. It's important that these B&G flo-controls are properly installed: the stem with the little lever needs to be upright. This flo-control valve is installed only in a vertical position, either at the top of a vertical pipe (where heat piping changes direction from vertical to horizontal) or in a horizontal heating pipe, but with the valve in an upright position. And the valve has to be installed with its flow-arrow pointing in the correct direction - in the direction off flow of heating water.
The valve handle is turned fully clockwise to prevent hot water circulation other than when the circulator is running. This is the normal setting for this control. When would we turn the lever counter-clockwise? We can think of several instances:
Watch out: B&G warns users to remember to return the lever to the "closed" (fully clockwise) position after the emergency or service. Otherwise you'll get un-wanted hot water heat circulation by gravity even if the room circulator is not calling for heat. Also, these valves sometimes leak around the packing nut below the flo-control valve lever. The valve instruction and service manual describes how to remove, clean, and repair the valve without disassembling system piping.
At References we provide a link to an excellent resource to understand these flow control valves: the B&G Flo-Control Valves - installation, operation, and service instructions manual from Bell and Gossett - an ITT company.
B&G Hydrotrol™ Check Valves
Bell & Gossett (and other manufacturers) also provide a separate Hydrotrol™ valve to prevent hot water from circulating in a building by gravity when the room thermostat is not calling for heat.
This brass valve includes a knob that permits bypassing this check valve with a simple half-turn, achieving the same emergency heat or service functions we described above.
The Hydrotrol HT flow control valve - a specialty check valve e is used to prevent hot water from circulating through a building where the boiler is kept on to provide domestic hot water via a tankless coil or indirect water heater, during non-heating-season months.
It is also installed to prevent overheating of individual heating zones by gravity. But unlike the red B&G Flo-Control valves discussed above, the Hydrotrol flo-control valve can be installed both vertically and horizontally in heating piping.
Internal Flow Control Valves - IFC Valves on Heating Circulator Pumps
Check valves may be present on a hot water heating system (hydronic heating) but may be less easy to spot.
IFC valves or "internal flow control" check valves are built right into the circulator pump of some models, including some circulators made by Taco® such as the Taco nnn-IFC® (nnn=model number and IFC = internal flow control) circulator pumps.
Taco's product literature comments on the benefits of an IFC type circulator pump:
Heating System Backflow Preventer Valves Protect Public Water Mains / Private Water Piping from Heating System Water Contaminants
Because a building potable water supply piping cold water line is used to deliver water to hydronic or steam heating boilers, we need to prevent heating system water from back-contaminating the building water supply piping.
At a hot water heating system a heating system backflow preventer check valve is used to keep hot, high pressure water in the hydronic heating system from flowing backwards through a boiler water feed line into the building water supply - a sanitation concern.
On both hot water (hydronic) and steam heating systems the backflow preventer may be built into the automatic water feed valve (photo at left, also see BACKFLOW PREVENTER, HEATER WATER FEEDER).
At our heater backflow photo (above left) the automatic water feed valve (red arrow) includes a built-in backflow prevention device.
Depending on local plumbing codes, a separate (from the water feeder valve) dedicated backflow preventer valve may also be installed "upstream" of the automatic water feeder - that is, between the heating system water feed valve and the incoming municipal water supply cold water piping (green arrow). A closeup of the separate heating backflow preventer is shown in a second photograph below.
The blue arrow in our photograph shows the direction of water flow into the water feeder and onwards into the heating boiler.
In sum, backflow preventers found on heating systems are installed to prevent higher-pressure heating system water from being forced backwards (say through a water feeder valve) into the building potable water supply piping.
Water Feeder Valves on Hot Water and Steam Heating Systems - as check valves
On older hydronic or steam heating boilers the expansion tank and water feeder valve are separate physical units (photo at left). This automatic pressure-reducing water feeder combines a check valve and boiler water feeder. Like the separate backflow preventer described just above, the check-valve function, internal to the automatic water feeder device, prevents back-flow of heating system water into the building water supply piping.
This bell-shaped device opens and sends makeup water into the heating boiler and its piping whenever the heating system's internal water pressure falls below a normal level.
The feed-pressure i s typically factor-set to 12 psi when the boiler is cold, but adjustable where higher starting water pressure is needed for taller buildings.
Systems without an automatic water feeder are less safe and risk serious boiler damage should boiler water be lost and should there be no low water cutoff installed on the system. See WATER FEEDER VALVES for details about water feed valves for hydronic boilers. Steam boiler automatic water feed valves are discussed at WATER FEEDER Valves, Steam
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).
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