PRIMUS boilers, both integral and standalone, require periodic preventive maintenance (PM) to operate at peak efficiency.

This blog will discuss the steps required to conduct a thorough PM.

Ensure all safety precautions are followed at all times during preventive
maintenance. Read all maintenance manuals, warnings, and instruction
labels before performing maintenance on any piece of equipment.

Preventive Maintenance Preparation

Required Tools, Equipment, and Supplies

  • Amp Probe
  • Multi-meter
  • Standard Hand Tools
  • Shop Vacuum
  • Long Scraper

Required Spare Parts

  • Heating Element Gasket Kit (PRIMUS P/N 801419)

PM – Required Steps

Water Quality

If the mineral content exceeds the following recommended limits, various external treatment processes (water softener, reverse osmosis, etc.) must be used to correct the problem. This option should be discussed with the supervisor responsible for maintaining the PRIMUS sterilizer. An aftermarket reverse osmosis system is available from PRIMUS for most sterilizer sizes.

An analysis of the on-site boiler feedwater should be made by PRIMUS
or a recognized and reliable water treatment company to ascertain the
existing feedwater chemistry.

Recommended Feedwater Quality

  • Hardness ppm 8 – 85 (~0.5 – 5 gpg)
  • P-Alkalinity ppm 85 – 410 (~5 – 24 gpg)
  • T-Alkalinity ppm 200 – 500 (~7 – 0 gpg)
  • pH (strength of alkalinity) 8.0 – 11.4
  • Specific Resistivity ~50k Ù cm (50,000 ohm-centimeters)

Blow down the boiler on at least a once-a-day basis. If the boiler feedwater is outside the above limits, a more frequent blowdown regimen is required.

Recommended Limits within a Boiler

  • Total Dissolved Solids ppm 3500
  • Total Alkalinity ppm 850
  • Suspended Solids ppm 300
  • Silica (SiO2) ppm 125
  • Sulfite (SO3) ppm 25–50
  • Phosphate ppm 30–60
  • P-Alkalinity as CaCO3 ppm 900
  • Iron ppm 2

Water quality can affect efficiency or result in boiler damage if neglected. Boiler feedwater contains impurities in solution and suspension. These impurities concentrate in the boiler since the steam generated is essentially pure. The concentration of these impurities increases as more feedwater is introduced into the boiler and steam is produced. If the suspended solids are allowed to concentrate beyond certain limits, a deposit or “scale” will form on the boiler’s internal surfaces. This deposit can interfere with proper boiler operation and cause boiler failure.

The concentration of these impurities is generally controlled by having the proper feedwater quality and by periodic boiler blowdowns. Blowdown refers to removing a portion of the boiler water with high solids concentration and replacing it with make-up water of a lower concentration.

General External Inspection

  • Inspect the outer casing and all plumbing for signs of water leaks
  • Inspect the boiler gauge for proper operation
  • If the boiler is an integral boiler, make sure the sterilizer plumbing is not leaking onto the boiler

Low Water Cutoff

  • Remove the low water cutoff probe and thoroughly clean it
  • Inspect the connecting wire for any damage and replace it, if needed
  • Make sure the probe is screwed tightly into the sparkplug and install it back into the boiler

Water Level Control Probe

  • Remove the low water cutoff probe and clean it
  • Inspect the connecting wire for any damage and replace it, if needed
  • Make sure the probe is screwed tightly into the sparkplug and install it back into the boiler

Check Valves and Feedwater Solenoid Valves

  • Inspect for wear and clean the two feedwater check valves. Replace them once a year
  • Inspect and clean the feedwater solenoid valve and install a valve kit, as needed

Sight Glass

Safety glasses and gloves should be worn at all times when
working with or examining the water gauge glass and connections.

Pressure in the generator must be at zero before proceeding.

Improper installation or maintenance of the gauge glass and connections
can cause immediate or delayed breakage resulting in bodily injury and/or
property damage.

  1. Apply Teflon tape or pipe dope to the pipe threads. Install the top gauge fitting (fitting without a drain valve) into the uppermost tapping. Wrench-tighten the fitting until it is snug and the glass outlet is pointing at five o’clock (about 1/8 turn from its final downward vertical position).
  2. Install the bottom gauge fitting (the fitting with a drain valve) until it is snug and the glass outlet is pointing directly upward. Verify the top and bottom fittings are threaded into the tappings with the same number of turns (distance A= distance B).
  3. Remove the glass packing nut, friction washer (or packing gland, depending upon the model), and the glass packing from the fittings. Place them in the same order onto both ends of the gauge glass. Push both packings about an inch up the gauge glass.
  4. Gently insert one end of the glass into the top gauge fitting. Keeping the glass inside the top fitting, gently rotate the top gauge fitting clockwise until it is vertically aligned with the bottom gauge. Insert the glass into the bottom fitting until the glass bottoms out on the shoulder inside the bottom fitting.
  5. Carefully raise the glass about 1/16″ and slide the lower glass packing down until the glass packing contacts the lower gauge fitting. DO NOT allow the glass to remain in contact with any metal!
  6. Carefully slide the upper glass packing up as far as possible.
  7. Hand tighten both glass packing nuts, then tighten 1/2 turn more using a wrench. Tighten only enough to prevent leakage. DO NOT OVER TIGHTEN! If any leakage should occur, tighten lightly, a quarter turn at a time, checking for leakage after each quarter turn.

Heating Element(s)

  • The sight glass should be checked daily to ensure that the boiler has adequate water.
  • A monthly inspection should be made of the internal wiring. All electrical connections should be checked for tightness.
  • A check for water leaks should also be made and any loose fittings immediately tightened.
  • Every four months, the low water cut-off and pump control should be checked to ensure that it is functioning properly.
  • Every four months, the probe and isolator should be checked for deposits and cleaned, if necessary. This is accomplished by removing the inspection plate, removing the probe (with a standard socket wrench), and cleaning and replacing the probe.
  • Every four months, the heating element(s) should be removed. If scale has begun to form, the element(s) should be cleaned and the boiler should be drained and flushed.

New bolts and a new gasket should always be used
when re-installing an element to assure proper sealing.

Operating Pressure and High Limit Pressure Switches

  • With no pressure in the boiler, remove the ¼ inch plug from the control switch piping manifold. This will drain out any debris.

Clean-up and Testing

  • Wipe down the outer boiler casing
  • Close all drain valves on the boiler
  • Make sure that water to the boiler is turned on
  • Turn the boiler on and let it fill with water
  • As the boiler is heating, use the amp probe to ensure all three legs of the heating element(s) are close to the same amperage. (Use all standard safety precautions when working around high voltage)
  • Check for any leaks and repair them
  • Start a sterilizer cycle and observe the boiler for proper operation

Have a question or having difficulties? Talk to Dave Schall, our PRIMUS sterilizer expert who is here to assist you anytime at 877.679.7800 extension 1212 or email at

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