Applicable Systems
Cleaver-Brooks Hawk 6000 Controller
Symptoms
Controller displays E3, indicating a high steam pressure alarm. The operating pressure limit controller has tripped at the setpoint, shutting down the burner to prevent overpressure of the boiler pressure vessel.
Possible Causes
- Pressure limit switch setpoint set too close to operating pressure
- Boiler load demand dropped suddenly causing pressure rise
- Safety relief valve stuck closed or improperly sized
- Steam distribution system blockage or closed isolation valve
Troubleshooting Steps
- Step 1: Check actual steam pressure on the main steam pressure gauge
Compare gauge reading with the limit switch setpoint - Step 2: Verify the operating pressure control and high limit switch settings
Operating control should be 5-10 psi below the high limit setpoint - Step 3: Inspect the safety relief valve for proper operation - test manually if equipped
Replace valve if it does not reseat properly after lifting - Step 4: Check steam distribution system for closed valves or blockages
Ensure all isolation valves are in correct positions for current load
How to Reset
To reset E3: 1) Allow steam pressure to drop below the operating pressure control setpoint. 2) The burner management system will automatically reset when pressure drops. 3) If manual reset is required, press the Reset button on the pressure limit controller. 4) Normal operation resumes as demand increases.
Common Replacement Parts
- CB-750-110: High pressure limit switch, manual reset, 250 psi (Verify setpoint is at or below MAWP of vessel)
- CB-750-115: Safety relief valve, 250 psi set pressure (Test annually per ASME code requirements)
- CB-750-120: Operating pressure control, adjustable 0-150 psi (Set 5-10 psi below high limit)
Frequently Asked Questions
- Q: What is the correct setting for the high pressure limit switch?
The high pressure limit switch must be set at or below the Maximum Allowable Working Pressure (MAWP) stamped on the boiler nameplate. For a CB-700-250, the MAWP is typically 250 psi. The operating control should be set 5-10 psi below this limit.
- Q: Why does my boiler trip on high pressure when demand drops?
When steam demand suddenly decreases, the boiler pressure rises quickly because the burner cannot reduce firing rate fast enough. Installing a modulating burner control system or adjusting the firing rate proportional band can help manage pressure during load changes.
Source: Cleaver-Brooks CB-700 Boiler Operation and Maintenance Manual, Form 750-250
Category: Boiler