Operating instructions
32
15 - TROUBLESHOOTING -HYDROSTAT HIGH LIMIT CONTROL AND LWCO
 Troubleshooting Flow Chart
Burner Will Not Fire See Flow Chart, this page.
No or Insuffi cient 
Domestic Hot Water
If installed with indirect water heater, insure end switch in relay box controlling indirect water 
heater is properly connected to Cable 2. This will insure domestic water calls are prioritized. If 
Cable 2 is not used, turn Economy Feature OFF.
House Will Not Get or 
Stay Warm
1. 
Check for air-bound radiators.
2. 
Check thermostat settings including heat anticipator settings (common on non-digital 
thermostats). 
3. 
Check Economy setting. Economy feature, like outdoor reset controls, lowers average 
boiler temperature and can slow or, in some cases, prevent the house from coming up to 
temperature. Move to lower setting.
Is Red LED 
(LOW WATER) 
On?
Is Yellow LED 
(HI TEMP) 
On?
Is Yellow LED 
(TARGET) 
On?
Is 
PURGE LED 
on?
Replace 
Control
Control is 
Sensing Low 
Water
Control is 
Sensing High 
Temperature
Boiler 
Reached 
Target 
Temperature
Boiler in Purge Mode 
and will not fi re until 
temperature drops to 
140°F. 
See Purge page 36.
Both red and yellow LEDs are off and there is call 
to fi re burner, there will be 120 VAC in terminals 
B1 and B2.
►120 VAC is not present, replace control.
CAUTION- ALWAYS ALLOW BOILER TO COOL BEFORE 
ADDING WATER
Burner will not fi re until low water condition is satisfi ed.
►Verify system fi lled with water.
►Verify sensor is inserted correctly into well.
 Note: Use of heat-conductive grease may interfere with contact          
 between spring clip and copper well tube.
►Verify control is tightly clamped to well.
Burner will not fi re until boiler water has dropped to high 
limit differential set-point (10° below high limit setting).
►Verify high temperature setting is correct
.
When ECONOMY function is active, control monitors 
heating demand and establishes Target boiler temperatures 
below high limit setting to conserve fuel. Burner will not 
fi re until boiler temperature drops to Target Temperature 
Differential.
YES
YES
YES
YES
NO
NO
NO
NO










