LARGER VIEW of an octopus furnaceProcedures for Inspecting Hot Water Heating Boiler Systems - Hydronic Heat

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Heating boiler inspection: This document presents the detailed sequence of steps to use when inspecting residential heating systems with focus on heating boilers and furnaces, on assuring completeness, accuracy, and on maximum heating system defect detection. The heating system inspection methodology involved is intended to be generalized to the forensic diagnostic inspection of any complex system in order to have the highest probability of detecting important safety or operating defects.

This sounds fancier than intended. Our object is to use an organized procedure for inspecting for defects, without losing the ability to discover unexpected problems as well. The methodology discussed includes both details specific to heating boilers (the full outline at "Contents") and more general complex-system inspection methods (listed immediately below).

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© Copyright Daniel Friedman 2008-1993 all rights reserved -- Tri-State ASHI Seminar -- Last update 08/03/2010 - first presentation November 6-7, 1993

Detailed Steps in the Sequence of Examination of Oil-Fired Hot Water Boilers

Viewpoint #4--Detailed close scrutiny of the equipment, after a few "sanity checks"
ASHI 9.1.A.1 The inspector shall observe ... heating equipment

Inspect before operating the boiler

What are we looking at? Form a working Definition: A system which heats the house. A steel, copper, or cast iron "box" of hot water, connected to a loop of pipe (and radiators or baseboards) which runs around through the living area. The same physical water stays in the boiler and is circulated by a pump so that heat is delivered to the living area. Burning oil makes hot gases which are used to heat the water before being exhausted outside. Pumps move fluids. Safety controls at various points protect against a number of potential hazards.

We include links to detailed heating system articles that explain how boiler or furnace parts and components work, how to inspect or repair them, and description of common problems that occur with each heating system component.

  • Do you see some reason not to turn this system on? (See SAFETY, HEATING INSPECTION.) What about other problems?
  • Is the system safely connected to a chimney?
  • Look at the temperature/pressure gauge: normal operating values?
  • Look for leaks in the boiler itself (Cast iron is more resistant to death by leaks than steel. Older cast iron systems without tankless coils, if shut off in summer, may be at risk of leakage and hidden damage. Steel rusts through. Cast iron cracks or leaks at joints.)
  • Look for leaks at controls now and again in the sequence below
  • Leaks at valves or fittings which drip into the jacket of a steel boiler or onto controls or zone valves risk failure and loss of heat.
  • Is there a tankless coil? If so, address both topics, looking at heating first, DHW second.

Examine components in the sequence of operation

Training in proper operation sequence of the 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 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.

The following 39 steps in a heating boiler operating sequence are discussed in more detail at BOILER OPERATING STEPS. Similar information is provided for warm air heating systems at FURNACE OPERATION DETAILS.

  1. Room temperature drops,
  2. room thermostat switches on ASHI 9.1.A.2 normal operating controls - see THERMOSTATS
  3. [zone valve opens and] circulator [starts] [except in Canada where circulators may be set up to run continuously and where the thermostat directly turns on the oil burner] [Circulator usually located on cooler return-side of the distribution piping loop-longer life.] - ZONE VALVES, HEATING
  4. boiler temperature and pressure are indicated on the TP gauge and should show increase not to exceed normal operating limits (200 deg F or less and less than 30 psi) - Gauges on Heating Equipment
  5. hot heating water leaves boiler passing by the ...
  6. air scoop (not always present; avoids air-bound baseboards)
  7. [air purge] (not always present; often leaky or sealed off)
  8. [automatic] water feeder (normally the manual valve for water supply to boiler is "on", the automatic valve is closed unless the boiler pressure drops below 12-15 psi. This valve is often also a backflow-preventer.) - WATER FEEDER VALVES, HYDRONIC BOILER
  9. expansion tank (waterlogged, dumping relief valve)(attic? no r v?=some old equipment) - EXPANSION TANKS
  10. [zone valve] (not always used, shorter life on the "hot" supply side of <->piping) - ZONE VALVES, HEATING
  11. distribution piping (watch for mineral salts indicating small clogged leaks)
  12. baseboards - which warm the room and thus the ... ASHI 9.1.A.6 heat distribution systems including fans, pumps, ducts and piping with supports, dampers, insulation, air filters, registers, radiators, fan-coil units, convectors - RADIATORS and AIR BLEEDER VALVES
  13. room thermostat senses the heat increase. Water passes - THERMOSTATS
  14. more distribution piping returning to boiler past
  15. zone service drain and [flow balancing valves] (are they leaky?) - ZONE VALVES, HEATING
  16. [circulator pump] (if it's not a convection system used on older houses) - Circulator Pumps & Relays
  17. back into the boiler.
  18. temperature in the boiler drops as cooler water returns.
  19. temperature sensor feels the temp drop and tells the ...
  20. primary control or high-limit control, but nothing happens (in the U.S.) until ...
  21. temperature drops 15 deg F below the HI setting on the primary control. Then the
  22. primary control turns on the oil burner (any drip/leak damage onto the control?) (Canadian systems: thermostat may activate burner directly.) - AQUASTAT CONTROL Functions
  23. burner pumps oil from the tank through ... (did we see the tank? is there an oil filter?)
  24. [copper] fuel line (and possibly sends excess back through a return line) See OIL TANK PIPING & PIPING DEFECTS or GAS PIPING, VALVES, CONTROLS depending on type of heating system fuel used.
  25. [past one or more Fire-o-Matic safety valves] (fusible link used in some jurisdictions) through the pump unit, sending ...
  26. high pressure oil to burner nozzle for spray into fire chamber (chamber ok?)
  27. transformer makes high voltage sent as spark to ignite oil (tar ooze at transformer?) and ...
  28. blower unit sends combustion air into the fire chamber... (is there adequate combustion air? how about when the boiler room door is closed?)
  29. Oil begins to burn (rough start or poor shut-down? smoke, soot, odor, noise ?) A flame sensor makes sure that combustion is occurring. CAD CELL RELAY SWITCH or Stack Relay Switch
  30. hot gases pass through tubes in steel or between sections in cast iron boiler, sending heat back into the heating water through the heat exchanger. (soot acts as insulation--boiler cleaned recently?)
  31. hot gases are collected at top of boiler and sent out through exhaust flue ...
  32. where the barometric damper assures proper and even draft; hot gases continue ..., up
  33. up the chimney to outdoors.
    ASHI 9.1.A.4 chimneys, flues, and vents (is the chimney improperly shared or vented to multiple floors?) ASHI 9.1.A.5 solid fuel heating devices [e.g. wood and coal stoves]
  34. boiler temperature rises up to the "HI" limit. (Thinking of High take a look for a pressure relief valve and look for defects there: leaking, corroded, not piped to floor, reduced diameter piping.) - RELIEF VALVE, TP VALVE, BOILER
  35. sensor informs Primary Control which turns off the burner-(sloppy shut down?) (Circulator is continuing to run)
  36. the room is warm enough according to the thermostat so the ...
  37. thermostat senses the temperature rise and opens its switch. (Special thermostat sophistication and functions excluded here)
  38. circulator stops (except in Toronto) - Circulator Pumps & Relays
  39. Oil or gas burner will either stop then or continue until HI limit (AQUASTAT CONTROL Functions) is reached. - OIL BURNERS and OIL BURNER NOISE SMOKE ODORS

Look closely at controls, peripherals, key components,

while going through the detailed sequence
ASHI 9.1.A.3 automatic safety controls
  • Combination control - combining High Limit and "Low Limit" (which may or may not be in use depending on presence of a tankless coil). See BOILER CONTROLS & SWITCHES for details.
  • High Limit and Low Limit (if tankless coil) separate controls on older equipment - Limit Switches, Boilers
  • Flame sensing device: Cad Cell or Stack Relay (watch for sensitive relays and learn about the re-stepping lever) - CAD CELL RELAY SWITCH
  • Automatic water feeder and Expansion Tank - EXPANSION TANKS
  • Pressure Relief Valve - RELIEF VALVES - TP VALVES
  • Pressure and Temperature gauge--12 psi cold, less than 30 psi hot. Over 30 psi dumps relief valve.(Typical operating temperature settings LO-120-160 HI-180-200 °F. Typical operating temperature observed at the gauge will be below the high, and can be as low as nighttime room temperature in non-heating season if no tankless coil is in use. The temperature/pressure gauge may help in checking for normal conditions before and during boiler operation. However the gauge can be wrong!) - Gauges on Heating Equipment
  • Tankless coil--leaks, missing mixing/tempering valve, relief valve (some jurisdictions). Risk of scalding water at the house sinks/tubs if there is no mixing valve. - TANKLESS COILS

Leaks and Corrosion - some implications

  • Surface rust--repairable. Clean when serviced and monitor
  • Exfoliation--very serious, possibly not repairable, risks loss of boiler.

Common Heating System Leak Locations

  • Coil mounting plate - see rust stains below and around plate
  • Pipe fittings at face of coil plate - mineral salts
  • Leaks around bolt openings - suspect hidden damage

Examples of understanding function and implications:

  • Leaks are never acceptable, anywhere on a heating system. Leaking relief valves need immediate attention and repair (Leaking relief valve could be due to water-logged expansion tank, improper control settings (temp too high), improper automatic water feeder operation (pressure too high), or defective valve (leaky). True, you only have to report the valve. Did you miss problems at the other components?) Corroded relief valves also need test and repair/replacement

    Do not touch the relief valve- it may open and fail to shut down.

    Do not pick at corrosion as you may start a catastrophic, un-stoppable leak requiring total system shut-down.
  • Different water pressure/flow observed in the kitchen: hot water pressure significantly less than cold--is a tankless coil installed? is a water softener installed? is there "hard" water--have mineral deposits clogged the coil? Are there "cleanout" plumbing fittings on the coil piping? Does this suggest a history of clogging and acid-flush treatments? Can a clogged coil be repaired or replaced? How severe was that rust you observed at the coil mounting plate?


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