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ZONE VALVES, HEATING
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 article series 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
Because on some hot water heating systems the check valve or flow-control valve is integrated into the circulator pump assembly, also see Circulator Pumps & Relays.
[Click to enlarge any image]
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.
Taco Flo-Chek Check Valves
Quoting from the company's product literature, the properties of this valve combine a check valve (don't circulate hot water when the system is not calling for heat) a the thumb screw that can be opened manually for gravity feed applications. This is a check valve, not a zone balancing valve.
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:
Manually-Operated Heating Zone Flow Control Valves
Our photograph at left shows three Taco hot water heating zone circulator pumps and three lever-type blue-handled heating zone flow control valves that are used to balance the flow of hot water among the three heating zones.
The two bottom valves are in the fully-open position (handle parallel to the heating water pipe) while the top valve is about half-way closed.
When all three heating zones are calling for hot water at the same time, that partly-closed valve reduces the heat flow into that zone.
Why would we do this? Well in most buildings heating zones are not all of the same length. Or zone areas may vary in their rate of heat loss - some needing more heat than others.
By using a manual heating zone balancing valve on each hot water heat zone piping we can tune the flow of heat to prevent some building areas from being too cold while others are too hot - when all of the zones are calling for heat at once.
In the installation shown at above left, the three lever-type ball valves, one on each zone, also make it easier to swap out a circulator pump assembly - if we can close off the heat piping on either side of the circulator pump we can change it out without having to drain down the system and without having to then force air out of the heating piping.
Below we illustrate Bell & Gossett's current heating zone circulator flow control and service valves, the company's Check_Trol valve. Quoting from the product literature:
Manually-Set Heating Zone Pipe-Mounted Heating Zone Flow Control Balancing Valves
A smaller and harder-to-spot manually-set hot water heating zone flow balancing valve is installed on some hydronic heating systems, usually where heat is provided by a single circulator forcing hot water through multiple zone valves.
Because heating zone piping and zone size or zone area heat loss may vary widely within an individual building, if we cannot regulate the hot water flow in individual zones we may find that when more than one of the thermostats are calling for heat at once, some building areas may be too cold while others may be too warm.
The heating system installer or service technician addresses this heat imbalance by fine-tuning the volume or the rate at which heating water is delivered to different building areas.
Notice our blue arrows pointing to those bronze & brass fittings just below each of the red-handled zone drains in our photograph? By loosening the lock-nut and using a flat-bladed screwdriver to open (CCW) or close (turn clockwise) these little valves, the service technician can balance the heating flow among multiple hot water heating zones.
Also see ZONE VALVES, HEATING.
Radiant Heat Flow Control Valves
Radiant floor heating systems provide water flow controls for individual heating zones or even tubing loops within zones. For example see the controls provided by
Variable Speed Circulator Motors Offer Heating Zone Flow Balancing Alternative
Below we show an UpStart hot water heating zone circulator pump produced by B&G (Bell & Gossett). This circulator pump includes a variable-speed circulator motor (see that gold knob on the electrical box atop the motor?). This was a four-speed motor whose output rate could be set by the consumer or heating service technician.
By slowing or speeding the motor we could slow or speed the flow rate of hot water through the zone managed by this circulator. The result: this control provided another way to balance heat flow among multiple zones (and circulators) in a building.
This circulator, the Bell & Gossett SLC-25 Upstart Circulator was sold during the 1980's and is not currently available. Control are also obsolete, but B&G offers similar replacements (such as the NRF-22). At below right is a newer but also obsolete product, the B&G NRF-VS variable speed circulator is shown.
Contemporary as well as obsolete variable speed circulator pumps from B&G, Taco & Grundfoss are detailed at CIRCULATOR PUMP RELAYS & OTHER CONTROLS.
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 VALVE, 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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