The Startup & Commissioning Checklist

You just took delivery of a new thermal fluid system. It is bolted down, wired up, and nearly ready to run. But the way you commission it will shape its safety, reliability, and service life.

A disciplined startup helps prevent nuisance trips, cavitation, seal and pump damage, contaminated fluid, hidden leaks, and avoidable downtime. The good news is that commissioning a HEAT system is straightforward when you follow the sequence and document the results. 

This guide walks through the process from installation readiness to stable operation. It explains why each step matters, what conditions signal that you are ready to move forward, and what baseline information to record for future maintenance and troubleshooting. 

Before You Begin: Applicability and Safety 

This guidance is intended for closed-loop, liquid-phase thermal-oil systems installed in accordance with approved project drawings and equipment documentation. Actual startup requirements vary with the selected heat transfer fluid, system volume, operating temperature, pump arrangement, expansion-tank design, controls, site piping, and applicable codes. Always follow the equipment-specific operation and maintenance manuals, approved drawings, fluid manufacturer’s recommendations, and site safety procedures for your system. 

Water/glycol systems share some of the same fundamentals, but the procedures and temperature thresholds below are primarily for heat transfer oils. Contact HEAT’s Service Department for water/glycol-specific guidance.

SAFETY FIRST

Thermal fluid systems may operate at temperatures up to or above 700°F. Before anyone works on or near the system, confirm that personnel are trained, authorized, wearing the required PPE, and following lockout/tagout and site safety procedures. Never bypass safety devices or operate outside approved design limits.

Consult your HEAT product manual for detailed instructions and specifics about your system's components.

The Pre-Startup Walkthrough 

Many startup problems begin with installation details that were missed before the heater was energized. Confirm these items first and the actual heat-up becomes much more predictable: 

• Fluid availability and storage. Confirm that the specified fluid and enough volume to fill the piping, equipment, and expansion tank are on site. Store drums indoors and protect them from standing water. 
• Piping pressure test. Pressure-test interconnecting piping before startup. For hot-oil service, use dry instrument air where permitted. Never pressure-test a hot-oil system with water because residual moisture can be difficult to remove and may flash to vapor during heat-up. 
• Design verification. Confirm that the selected fluid is suitable for the design temperature and that the installed system matches the approved drawings and equipment documentation. 
• Drains and vents. Provide low-point drains and as many practical high-point bleeds as possible. Air collects at the high points, and poor vent access can add hours or days to startup. 
• Expansion-tank arrangement. Locate the tank at the highest process point where practical. If it must be pressurized, verify applicable code requirements, including ASME construction above 15 PSIG, and route the vent or relief discharge to a safe location. 
• Electrical and mechanical inspection. With power isolated, check electrical connection torque, continuity, grounding resistance, and piping-bolt torque. Confirm access to safety devices, vents, suitable containers, and required instruments. 
• Pump alignment. Re-align long-coupled pumps after the skid is permanently placed, to within ±0.002 in. HEAT aligns these pumps during the factory acceptance test, but shipment can disturb alignment and the coupling is shipped separated from the pump shaft. Do not disturb factory-aligned close-coupled or sealless pumps. 

Step 1: Fill From the Bottom Up 

Always fill from the lowest practical drains in the complete system, not from the expansion tank or another high point. Bottom-up filling pushes air toward the high-point vents.

If several low points exist, alternate among them for a more even fill. Remember that the low points on the HEAT skid may not be the lowest points in the complete installation, especially when equipment is installed on a mezzanine. 

• Use virgin fluid. Charge the system from a drum pump or a HEAT Pump/Filter System (PFS-III). 
• Open the flow path. Open the fill/drain valve, required isolation valves, and every air-bleed valve. Station personnel with suitable containers at each bleed. 
• Close bleeds as fluid arrives. Pump fluid into the system and close each process-side bleed after fluid reaches it without air. 
• Stop near 25%. When the expansion tank is approximately one-quarter full, stop filling and close the fill/drain valve. This assumes the expansion tank is correctly sized. 
• Let the system settle. Wait several minutes, then carefully crack the bleed valves to release residual air.

Step 2: Confirm Pump Rotation 

Never run a pump dry or backward. When practical, verify rotation before coupling the pump to the motor. With the system filled and control power available, momentarily tap the green pump-start button so the motor only bumps. Observe the motor fan and compare its direction with the arrow on the pump casing. 

If rotation is incorrect, isolate power and have qualified personnel swap the appropriate motor leads at the starter. Then repeat the check before sustained operation.

WARNING: Do not run the pump backward or without fluid in the system. Either condition can cause serious internal damage.

Step 3: Remove Trapped Air 

Accessible high-point vents are one of the most important ingredients in a clean startup. Air is less dense than the fluid, so it collects at the top of the piping and equipment. Without a vent at those locations, removal becomes much more difficult. 

• Bleed the HEAT skid first. Open the vents on heat exchangers and the heater-chamber vent line until only fluid flows, then close them. 
• Move through the process piping. Repeat the procedure at every accessible high point. 
• Bleed dynamically. Start the pump and repeat the bleed sequence while the fluid circulates. 
• Watch discharge pressure. If the pump cavitates and pressure falls, stop the pump, allow the fluid to settle, and repeat until discharge pressure remains steady. 
• Set the nitrogen blanket. If the expansion tank has a nitrogen blanket, open its manual vent, sweep nitrogen through the tank for five minutes, close the vent, and confirm regulator pressure after air has been removed from the process piping. 

Without adequate high-point bleeds, the atmospheric expansion tank may become the only escape path for air, and the process can take many hours. Contact HEAT’s Service Department if stable circulation cannot be achieved.

Step 4: Raise Temperature in Controlled Stages 

Do not jump directly to the operating setpoint. A controlled heat-up removes remaining air and reveals hidden moisture before it can create a larger problem. 

• Set the high-temperature switch. If adjustable, set it 25°F above the intended operating temperature. Most switches are preset at the factory. 
• Start at 150°F. Energize the heater only when the pump is running, the controller is calling for heat, and the over-temperature switch is not tripped. Hold at 150°F while monitoring for air and cavitation, and continue bleeding until circulation is stable. 
• Stabilize at 200°F. Increase the setpoint and allow the system to settle before approaching water’s boiling point. 
• Use small steps near 212°F. Move in 5–10°F increments. Set 210°F, verify stable discharge pressure, and hold for at least 10 minutes. Then increase to 220°F and hold for 10 minutes while watching for moisture-related cavitation. 
• Reach 250°F carefully. Continue in 10°F increments until the system remains stable at 250°F for 30 minutes. 
• Continue to the target. After the 250°F hold, increase in 50°F increments to the operating temperature. 
• Record the baseline. Operate at the target temperature for at least 30 minutes without vapor or boiling. Record incoming voltage, heater amperage, motor amperage, discharge pressure, and process delta-T. If a cooling cycle is provided, operate it and record that data as well.

Step 5: Monitor the Expansion Tank and Finish the Hot Inspection 

Watch the expansion-tank sight glass throughout heat-up. Maintain the level between approximately one-quarter and three-quarters, topping off through the fill/drain connection as required. 

• Cloudy or milky fluid indicates moisture. Continue controlled heating until the fluid clears. If it does not clear, replace it or filter it through equipment such as the PFS-III. 
• Abnormal expansion or surging indicates trapped air or steam. Recheck the bleed points. If the condition persists, de-energize the pump and inspect again. 
• Healthy heat transfer fluid is amber. Record the color as a visual baseline for future inspections. 

Keep valves and flanges uninsulated through initial heat-up. After the system reaches full operating temperature, inspect every joint for leakage and complete the final torque pass after thermal expansion has stabilized. Insulate only after these checks are complete.

Premature insulation can conceal a leak, and oil-saturated insulation creates a fire hazard.

How to Know Commissioning Is Complete 

A successful commissioning may require several heat-up, settling, and bleeding cycles. System volume, piping geometry, vent locations, ambient conditions, and the amount of trapped air or moisture all affect the schedule. Completion should be based on system condition, not speed. 

• Stable circulation. Discharge pressure remains steady without signs of cavitation. 
• Clear, healthy fluid. The fluid is free of visible moisture and abnormal surging. 
• Leak-free joints. All valves, flanges, and connections have been inspected at full operating temperature. 
• Repeatable operating data. Electrical and thermal readings remain stable and provide a usable baseline for future comparison. 
• Corrective items documented. Any remaining issues, responsibilities, and follow-up actions are clearly recorded.