Functional Testing for Boilers

Functional Testing for Boilers. 1

Functional Testing Field Tips. 2

Key Commissioning Test Requirements

Key Preparations and Cautions

Time Required to Test

Testing Guidance and Sample Test Forms. 6


Functional Testing for Boilers

Functional Testing Field Tips

Key Commissioning Test Requirements lists practical considerations for functional testing. Key Preparations and Cautions address potential problems that may occur during functional testing and ways to prevent them.

Key Commissioning Test Requirements


The performance of a boiler and the hot water system is acceptable if it meets the design intent and specified operating sequence. Attention to the following actions during the commissioning process can result in significant improvements in system operation and energy efficiency:

Safeties, Interlocks, and Alarms

All safeties, interlocks, and alarms operate correctly in both automatic and manual operating modes. Verify proper sensor installation and calibration. The DDC control system relies on input from various sensors (such as temperature, pressure, and flow) in order to achieve the desired system operation. If sensors are not located correctly, or the measured value from any sensor to the control algorithm is incorrect, the system will not respond as intended.

Actuation and Sequencing

Verify that automatic isolation valves are installed and operate correctly, if applicable. (Automatic isolation valves are typically installed when multiple boilers are connected to a common supply header. Boilers with dedicated pumps generally do not have automatic isolation valves.) When an individual boiler is not operating, the isolation valve should be closed to prevent water from circulating through the unit. This configuration reduces pumping energy and prevents dilution of the hot water temperature by blending unheated water, flowing through the non-operational boilers, with hot water, coming from the operating unit(s).

Verify proper boiler staging under normal operation, as well as under all failure and emergency operating modes, especially if multiple units are installed which are unequal in size. Close coordination between boiler staging and actual load will minimize energy usage. For example, it is beneficial to use a small boiler with good turn-down efficiency to meet low loads and to enable a larger boiler only when the load surpasses the heating capacity of the smaller boiler. When this occurs, the small boiler will be sequenced off until load exceeds the large boiler capacity, then both boilers would operate to meet the load.

Verify that the boilers and primary/feed water pumps stage up and down per the sequence of operations under all operating modes.

Verify that the time delay between boiler start/stop commands are per design.

To remove residual heat from the boiler, the primary/feed water pump operation time delay, after the boiler is commanded OFF, is per design.

Verify that the automatic isolation valve(s) associated with the respective equipment opens fully upon start-up and closes fully upon shutdown after the specified time delay has expired.

Setpoints and Reset Controls

Verify that the system operates and maintains hot water supply temperature setpoint under all operating modes, including automatic, manual, and failure/emergency modes.

Verify proper coordination between individual setpoints and reset strategies. For example, the hot water temperature reset and air handling unit discharge air temperature rest control strategies are compatible. Without coordination between hot water temperature reset and discharge air temperature reset, the air handler may be trying to make hotter air than is possible with the hot water supply temperature. This situation would result in boilers being staged ON even though there is no load on the system, wasting a significant amount of energy.

Verify that the control algorithms generate the proper water temperature setpoint based on the reset parameters specifies in the sequence of operations.

Verify that the reset parameters are optimized for the system. In addition, ensure the reset control strategy does not result in a return water temperature from the building loads, which can cause the flue gasses to condense in non-condensing boiler systems.

Verify that the O2 trim controls, if applicable for a specific project, operate to ensure that excess oxygen in flue gas is maintained at setpoint. If O2 trim controls are not installed, review flue gas report and verify the boiler was tuned at high-fire and at least one intermediate part-load operating point.

Control Accuracy and Stability

Verify that all control loops stabilize within a reasonable amount of time (typically 2 to 5 minutes) after a significant load change such as start-up or automatic/manual recovery from shut down.

Some projects may require full-load capacity and part-load turndown performance testing. Tests should be performed when the loads generated can be dissipated adequately. Verify the boiler meets the manufacturer’s stated part load performance under actual operating conditions.

Key Preparations and Cautions

Prefunctional Checklists and Start-up

Prefunctional checklists should be completed throughout construction, during normal commissioning site visits, as installation of the various components and systems are completed. Sensor and actuator calibration, control point checkout, and boiler/piping flushing is typically considered to be part of the prefunctional checklist.

In addition to the prefunctional checklists, all manufacturer-required component start-up procedures must be complete in order to conduct functional test procedures. Local codes should also be reviewed to ensure any required start-up and testing procedures are performed prior to long-term system operation. Both the air-side and water-side TAB must also be complete prior to functional testing.

Successful execution of the hot water system functional tests is dependent on the operation of ancillary equipment (air handling units, terminal units, and distribution pumps). At a minimum, the prefunctional checklist should be completed on the components/systems served by the boilers and should be capable of safe, temporary operation. Final boiler system testing should not be performed until all of the associated systems are fully operational, including chemical treatment and make-up water controls, if applicable. Final boiler system testing can be best achieved through trending under normal operation.

Test Conditions, Considerations and Cautions

Ideally, functional performance testing, including capacity testing if required, would occur during the heating season, so that the entire system can be observed under normal operating conditions without seriously overheating the building. Construction work in the building could be adversely affected if the space temperature deviates significantly from a tolerable level. If this is not possible due to the construction schedule, system operation and performance must be verified by either creating false loads on the equipment or through manipulation of setpoints to accommodate existing atmospheric conditions. For example, a heating load can be simulated by increasing all setpoints to be 10 ºF above current ambient conditions and allowing the system to respond accordingly. Care should be taken so that elevated temperatures do not have an adverse impact on other building systems or the spaces served by the equipment being tested.

The following points should be noted to avoid testing complications:

1 Valve leakage tests and tests that are targeted at verifying valve stroke, spring range, and sequencing should be conducted with the pumping system operating at its peak differential pressure. The differential pressure across the valve plug can impact the close-off rating and shift the operating spring range of the valve. These tests should be performed prior to temporary system operation to ensure that equipment will not be damaged during functional testing.

2 All resets, except the one being tested, should be overridden to prevent unwanted system interaction during testing. Once the specific reset control strategy has been verified, the remaining resets should be reinstated. System operation must then be monitored to ensure all control processes remains stable. This verification is best accomplished through trending under normal operation.

3 Integration of temperature setpoints must be coordinated between the boiler and equipment served. This is best illustrated through the following example: The water temperature setpoint is reset to 120°F, but the discharge air temperature setpoint for an air handling unit is reset to 130°F under the same operating conditions. The hot water coil control valve will modulate wide open because the AHU will never meet a 130°F setpoint with 120°F water, This scenario can result in excess water being pumped through the system, and possibly even bringing more boilers on-line to meet a load that does not exist.

4 Coordination between hot water temperature and coil design should also be checked. It is possible that the air temperature coming off the coil may not meet setpoint due to design limitations of the coil itself. Preferably, this issue is addressed during design-phase commissioning.

5 If the hot water temperature reset strategy is tested when there is minimal to no heating load, make sure to test the low end of the reset (coldest hot water supply temperature) first in order to minimize test time. It is easier and faster to add heat to the loop rather than to try and take it out when there is very little load on the system.

6 Safety and interlock tests, as well as some test procedures and loop tuning efforts (for example, high limit cut-out set points, emergency shut-down procedures, and failure/back-up system operation) could place the system at risk if the sequences do not function as intended. Appropriate precautions and procedures should be in place to protect personnel and machinery. These should include plans for quickly aborting the test if necessary.

7 If the boiler system is tested during off-peak months, ensure that the spaces served by the respective air distribution systems (air handling and terminal units) do not exceed safe temperatures. Often systems will be tested while construction is still being completed in the spaces being served. Elevating space temperatures well above ambient conditions may cause discomfort or create unsafe working conditions.

Instrumentation Required

Instrumentation requirements will vary from test to test and typically will include, but are not limited to, the following:

Temperature measurement devices (hand-held devices to calibrate existing sensors)

Differential pressure measurement devices (to test installed flow meters)

Combustion analyzer (for testing combustion efficiency or O2 trim controls)

Flow measurement devices (installed or hand-held devices to measure water, steam, or fuel flows)

Data loggers (to supplement existing sensors to verify system operation)

Time Required to Test


The amount of time necessary to execute functional tests on a hot water system is dependant upon the size and complexity of the installation and specified control sequences. For example, the number of system components (such as boilers and pumps), as well as the complexity of the sequence of operation (including reset strategies, capacity controls, staging parameters, and safeties/alarms) will significantly impact the time associated with testing the entire system.

For this reason, time estimates have been separated by component on a per unit basis as well as on an overall system level. Component-level tests typically refer to discrete functions of each piece of equipment (such as start/stop procedures, safeties, operational and failure interlocks, and alarms), where system-level tests focus on evaluating proper integration of each component to satisfy the desired control strategy (including staging, setpoints and reset strategies).

Component Level Testing

Two to three hours is needed per boiler.

Plan one to two hours per primary/feed water pump (refer to the Pumping module for secondary/distribution pump checkout).

One hour or less is needed per isolation valve, including individual stroke from fully open to fully closed (refer to the Pumping module for secondary/distribution pump checkout).

Variable: Full load capacity testing of a boiler can require many hours and several team members to set up and monitor all of the necessary operating points.

System Level Testing

Two to three hours will be needed to verify proper capacity or O2 trim control strategies.

Allow two to three hours to verify proper boiler staging, but testing time can be shortened if equipment start/stop time delays are set to minimum acceptable values.


Testing Guidance and Sample Test Forms

Boiler System Test Guidance

This testing guidance describes the steps and potential issues that may arise during testing.  Since commissioning providers typically have their own style of forms, the Test Guidance is not provided in a field-ready form.  Commissioning providers may use the Test Guidance to expand and improve upon their existing forms.  Example tests based on the Test Guidance documents are provided where available.

Test ID

Testing Guidance

(View Appendix D for Test Descriptions)


(View Appendix E for Source Details)

Example tests


Pump Performance and Impeller Trim Analysis


Hot Water System Pump Test  (Test ID 1009)

Chilled Water System Pump Test (Test ID 1010)

Condenser Water System Pump Test  (Test ID 1011)


Valve Leak-By




Radiant Floor Heating




Writing a Functional Test (general guidance)


Blank Test Form for Writing a Functional Test (Test ID 1015)

Example for Writing a Functional Test (Test ID 1020)

Boiler System Sample Test Forms

This table lists publicly-available sample tests from a variety of authors. Some of the tests are written for a specific building, while others are written for a general case.   This list of sample test forms also includes the Example Tests listed in the Testing Guidance table above.

Test ID

Test Forms

(View Appendix D for Test Descriptions)


(View Appendix E for Source Details)

Boiler System Prefunctional Checklists


Boiler Prefunctional Checklist



Boiler Prefunctional Checklist


Boiler System Prefunctional Checklists and Functional Test Procedures


Boiler System Functional Test



Standard Functional Tests for Heating Water Systems



Verification and Functional Performance Test Plan for EMS

PG&E/Malek & Caluwe

Boiler System Functional Test Procedures


Packaged Boiler Functional Test



Packaged Boiler Control Sequences



Data Collection Procedures for Hot Water Heating Pumps


Component-Level Prefunctional Checklists


Pump Prefunctional Checklist



Calibration and Leak-by Test Procedures



Fan-Coil Unit Prefunctional Checklist



Heating Water Piping Prefunctional Checklist


Component-level Functional Test Procedures


Cabinet Unit Heater Functional Test



Fin Tube Radiator Functional Test



Heating Fan Coil Unit Functional Test



Unit Heater Functional Test



Hot Water System Pump Test  



Chilled Water System Pump Test



Condenser Water System Pump Test