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AIR CONDITIONING & HEAT PUMP SYSTEMS
BACKDRAFTING HEATING EQUIPMENT
BACKUP HEAT for HEAT PUMPS
BANGING HEATING PIPES RADIATORS
BLOWER FAN OPERATION & TESTING
BOOKSTORE - InspectAPedia
BTU USAGE MONITORS
CARBON MONOXIDE - CO
CIRCULATOR PUMPS & RELAYS
DIAGNOSTIC GUIDES A/C / HEAT PUMP
DIAGNOSE & FIX HEATING PROBLEMS-BOILER
DIAGNOSE & FIX HEATING PROBLEMS-FURNACE
DIRECT VENTS / SIDE WALL VENTS
DRAFT REGULATOR, DAMPER, BOOSTER
DUCT SYSTEM & DUCT DEFECTS
ELECTRIC MOTOR DIAGNOSTIC GUIDE
FAN, AIR HANDLER BLOWER UNIT
FLOODED HEATING EQUIPMENT REPAIR
FLUE SIZE SPECIFICATIONS
GAS BURNER FLAME & NOISE DEFECTS
GAS PIPING, VALVES, CONTROLS
GEOTHERMAL HEATING SYSTEMS
HEAT PUMPS, DIAGNOSIS, REPAIR
HEATING COST SAVINGS METHODS
HEATING OIL PIPING TROUBLES
HEATING OIL TANKS
HEATING SYSTEM NOISES
HEATING SYSTEM TYPES
GAS LP & NATURAL GAS SAFETY HAZARDS
MANUALS & PARTS GUIDES - HVAC
MIXING / ANTI-SCALD VALVES
MOTOR OVERLOAD RESET SWITCH
NOISE, HEATING SYSTEMS
ODORS FROM HEATING SYSTEMS
OIL FILTERS on HEATING EQUIPMENT
OIL FILL PIPE LEAKS
OIL SPILL CLEANUP / PREVENTION
PLASTIC PLEXVENT ULTRAVENT RECALL
PUFFBACKS, OIL BURNER
RELIEF VALVE LEAKS
RESET SWITCH, HEATER PRIMARY CONTROL
RESET SWITCH, ELECTRIC MOTOR
RESET SWITCH, STACK RELAY
SAFETY, HEATING INSPECTION
SAFETY RECALLS CHIMNEYS VENTS HEATERS
SOLAR HEATING SYSTEM DESIGNS
SOOT on OIL FIRED HEATING EQUIPMENT
STEAM HEATING SYSTEMS
THERMOSTATS, HEATING / COOLING
VIDEO GUIDES: HEATING SYSTEMS
WINTERIZE A BUILDING
WOOD, COAL STOVES & FIREPLACES
WOOD STOVE SAFETY
ZONE VALVES, HEATING
How does a heating boiler work - what are the steps in its operating sequence? This article describes how a hot water heating system (hydronic heat) actually works, step by step, to heat a building. An understading of the sequence of steps in the operation of a heating system, from the moment that a thermostat calls for heat until the moment that the thermostat stops calling for heat can help us diagnos and fix many heating system problems.
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Training in proper operation sequence of heating system equipment and in the function of its controls is a step towards technical correctness. If you do not understand how a mechanical system works you cannot reliably expect to observe missing or defective components. This discussion is an exercise using sequence of operation to work for completeness. It is not technically exhaustive, it focuses on a specific example: oil-fired hot water, zoned, heating system.
Examine the accessible parts of the heating system. Let your eye travel from component to component in the sequence of operation. Apply the inspection logic discussed earlier, at each step. Consider the implications should each component be missing, damaged, inoperative, leaky, noisy, sooty, repaired by an amateur, etc.
Think through the operating sequence as you examine each component in that order. The following are the steps in one common set-up. This list is lengthy and detailed. The actual visual examination may take only a few minutes.
What follows is a detailed, step by step description of how a heating boiler works. We name each heating system component and what it does, in the order that heating system components operate during the heating cycle.
Items shown in [brackets] are ones which may not be present on some heating systems. We include links to technical articles that explain the operation of various heating system components and parts.
The following steps in a heating boiler operating sequence are discussed as part of a complete heating system inspection procedure for hydronic or hot water heat beginning at HEATING BOILER INSPECTION GUIDE. For steam heating systems, details are at STEAM HEATING SYSTEMS. Similar information is provided for warm air heating systems at FURNACE OPERATION DETAILS.
Comparing Operation of Heating Boilers in Canada and the U.S. - Continuous versus Intermittent Hot Water Circulation
On a typical oil fired heating boiler in the U.S. the wall thermostat is controlling the hot water circulator, turning it on or off. It is the temperature of the water circulating through the system (sensed at the primary control on the heating boiler) that actually turns the oil burner on or off to re-heat the water. That's why the wall thermostat is not an "accelerator" and that's why if the thermostat has been set to 60 °F., and the room temperature is at 60 °F., and we want to warm up to 68 deg.F., we just need to set the wall thermostat up to 68 deg.F. Setting the thermostat higher than that will not warm the room faster.
On a typical oil fired heating boiler in Canada where temperatures are cooler for more of the year, the circulator pump may be wired to run continuously all during the heating season, whenever power is turned on at the boiler. On these systems, the wall thermostat turns the oil burner on or off directly in response to room temperature.
This design tends to produce more even temperatures in the home, and it has an advantage which should be considered by anyone who owns an older home where drafts or poor insulation mean that there is a high risk of freezing heating pipes (freezing can occur in a heating distribution pipe, baseboard, or radiator when heat temperatures are set low and some corner or elbow or location of piping is exposed to very low temperatures.
If heating pipes freeze the result is loss of heat even if the boiler and circulator try to turn on, which in turn means there is risk of burst piping, water damage, mold contamination, or other costly problems. By forcing the water in the heating system to circulate continuously the risk of this freeze-up is greatly reduced.
This heating boiler operation article series answers most questions about central heating system troubleshooting, inspection, diagnosis, and repairs. We describe how to inspect, troubleshoot and repair heating and air conditioning systems to inform home owners, buyers, and home inspectors of common heating system defects.
The articles at this website also describe the components of a home heating system, how to find the rated heating capacity of an heating system by examining various data tags and components, how to recognize common heating system operating or safety defects, and how to save money on home heating costs. We include product safety recall and other heating system hazards. The limitations of visual inspection of heating systems are described. We continue to add to and update this text as new details are provided. Contact us to suggest text changes and additions and, if you wish, to receive online listing and credit for that contribution.
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