HydroTherm boilers troubleshooting

There are tons of things that can cause a gas boiler to break down: from improper use to faulty design. Manufacturers strive to produce perfect products, so internal faults do not occur frequently. A boiler is more likely to stop because of internal factors, many of which users can detect without calling a professional technician. Refer to the table below, which describes signs of malfunctions, and make your boiler operational again.

HydroTherm 70-195 boilers troubleshooting

Burners not functioning. 1. No power. 1. Check line voltage wiring and fuses.
2. Limit not working. 2. Check wiring and contacts, relay, temperature setting. Clean and adjust as necessary.
3. Flame rollout switch open. 3. Replace switch. Locate cause and correct.
4. Blocked vent switch open. 4. Reset blocked vent switch. Locate cause and correct.
5. Gas off at boiler gas valve. 5. Start boiler using Lighting/Operating Instructions.
6. Gas off external to boiler. 6. Check any gas valves in the line.
7. Plugged orifice spuds. 7. Check, clean and re-install.
8. Defective gas valve. 8. Troubleshoot intermittent ignition gas valve. Replace if necessary.
9. Improper wiring. 9. Check and correct in accordance with wiring diagrams.
10. Vent damper malfunctioning. 10. Refer to vent damper manufacturer’s instructions. Replace if necessary.
Burners will not shut down. 1. Defective gas valve. 1. Troubleshoot intermittent ignition gas valve. Replace if necessary.
2. Short circuit. 2. Check and correct wiring.
Flashback or burning at orifice spuds. 1. Manifold gas pressure too low. 1. Adjust to proper pressure.
2. Improperly sized/drilled orifice spuds. 2. Install correct spuds.
3. Leaking gas valve. 3. Replace valve.
4. Burrs on orifice. 4. Remove burrs.
5. Low supply gas pressure. 5. Contact gas supplier if natural gas. Adjust regulator if LP gas.
6. Excessive downdraft or draft problems in boiler room. 6. Check air supply, ventilation and venting system.
Delayed ignition. 1. Insufficient pilot flame. 1. Increase pilot gas flow.
2. Pilot burner/orifice clogged. 2. Clean pilot burner and orifice.
3. Overfiring. 3. Reduce rate to input on rating label.
4. Misaligned burners or pilot. 4. Realign burners or pilot.
5. Draft problem in boiler room. 5. Check air supply, ventilation and venting system.
Excessive condensation in vent. 1. Underfiring. 1. Increase rate to input on rating label.
2. Limit (Aquastat) set too low. 2. Reset Aquastat to higher setting.
3. Vent pipe too long. 3. Reposition boiler to reduce length.
4. Inadequate chimney or venting system. 4. Check chimney and venting recommendations.
Boiler not heating properly. 1. Underfiring. 1. Increase rate to input on rating label.
2. Limit set too low. 2. Reset Aquastat to higher setting.
3. Air in system. 3. Vent air from all points in system.
4. Circulator malfunctioning. 4. Check circulator, replace if necessary.
5. Circulation system clogged. 5. Shut down and cool boiler, drain and flush system.
6. Incorrect thermostat heat anticipator setting. 6. Adjust heat anticipator.
Fumes or gas odors 1. Leaks in gas piping or fittings. 1. Locate and repair or replace.
2. Leaks in gas service line or meter. 2. Shut down boiler and notify gas provider.
3. Obstructed chimney. 3. Check, repair and/or clean chimney.
4. Obstructed flueways or vent. 4. Clean flueways or vent and remove obstructions.
5. Undersized chimney or vent, high draft loss in vent. 5. Check National Fuel Gas Code and vent manufacturer’s recommendations.
6. Draft problem in boiler room. 6. Check air supply, ventilation and venting system.
7. Overfiring. 7. Reduce rate to input on rating label.
8. Vent damper malfunctioning. 8. Refer to vent damper manufacturer’s instructions. Replace if necessary.

HydroTherm GX SERIES boilers troubleshooting

Problem Detected Problem Solution
ER1 On Display The Safety High Limit of 215°F, 102°C, has been reached. 1. Check to see if water is dripping on the sensor.
2. Reduce the Hi setting (and/or) ensure that there is proper water circulation in the system.
ER2 On Display Water Probe… The water probe is transmitting an invalid signal – closed circuit. Check wiring
ER3 On Display Water probe…Sentry is sensing an open circuit at water probe. Or, the wiring to the outdoor probe is grounded. Check wiring. (Note: ER3 will be displayed if temperature sensed is less then 32°F, 0°C.) Note: If problem is corrected by resetting power, Sentry control had locked-up; contact Hydrotherm.
ER5 On Display DHW Problem The control has determined an Indirect water heater problem; the boiler has cycled off 10 times during a single call for domestic. The Indirect call will now be ignored until power is reset or the indirect call is interrupted. 1. Not enough flow to keep boiler from tripping on limit. Verify that a min. of 6 GPM. 0.4 Us, flow is going through boiler & indirect circuit.
2. Reduce indirect Aquastat setting, or Increase difference between (Lo Setting) and (indirect Aquastat setting).
3. Indirect limit or wiring failure.
ER6 “Flame Lock Out” Sentry has sensed a lack of 24V to the gas valve during operation or a Fenwal ignition lockout. 1. There is a problem in the ignition sequence; it could be caused by a faulty igniter, flame sensor, gas valve or improper line pressure or combustion. Check ignition sequence to determine which component is not functioning. (Sentry will retry ignition sequence
1 hour after ER6 code originally occurs or if control is reset)
2. Check for 24V between B on terminal block and F1 on Sentry plug, if not present a limit has tripped (see wiring diagram).
3. the Flow Switch on the GX-400 is also in the 24V circuit. Check for proper water flow and flow switch operation.
Burner shuts off before set-point temperature is reached (and burner light goes out) Reset calculation being used to lower HI setting. If OD probe is being used, the HI setting will be calculated using formula in Section 8.
Thermostat is satisfied 1. If the thermostat demand light is turning off, the thermostat has satisfied.
2. If DHW temp light is turning off; the aquastat or call for domestic has been satisfied.
ASO Indicates that the Air Switch is Open This is displayed when the boiler is expecting the air switch to be closed by a differential pressure generated when the combustion blower turns on. It can occur momentarily during normal operation. A problem is indicated when ASO is displayed continuously. 1. Are the vinyl tubes connected between the air switch and the ports on the inlet pipe. Negative side of switch connects to the port on the 1 1/2 in, 38 mm, ABS elbow.
2. Check for blockage on the intake and exhaust vents.
3. If fan is running, air switch may be faulty, ensure that it’s set for 0.2 in, 5.1 mm WC. The GX-400 condensate drain switch must be set at 3 in, 76 mm WC.
4. If fan is not running, check 120V wiring to blower, if ok remove low voltage harness from blower, if blower fails to start, replace blower, if blower does start problem may be with blower or Sentry control.
ASC Indicates that the Air Switch is Closed This is displayed when the boiler has turned the blower off and is expecting the air switch to be open. It can occur momentarily during normal operation. A problem is indicated when ASC is displayed continuously. 1. Is the fan running. If so check for 24V between C and D terminals, see wiring diagrams. If 24V is not present replace transformer.
2. Check venting termination with required venting described in manual.
Ignition Sequence not activated when burner light is on (Fan is on and Fenwal not flashing) Check for 24 Volts between terminal B1 on Sentry & Ground. 1. If there is 24V, indicates faulty wiring between Bl and W1 on Fenwal, or faulty Fenwal.
2. If 24V is not present proceed to next step.
Check for 24 Volts between terminal F1 on Sentry & Ground. 1. If 24V exists here but not at B1, indicates faulty relay inside Sentry, contact NTI, replace control.
2. If 24V is not present check for 24V at transformer.
3. If 24V exists at transformer, check wiring and safety limits. If 24V not present at transformer, check wiring and replace transformer if necessary.
Water Safety Limit trips (Automatic reset) Located in the supply manifold inside the boiler cabinet. May be caused by an error in the reading of the water temperature by the Sentry control. Watch cycle, and ensure the Sentry is displaying the correct water temperature and is modulating.
This device protects the boiler from overheating due to a lack of flow passing through the unit when the burner is on. FLOW MUST NEVER BE BLOCKED BY ANY VALVES INCLUDING MIXING OR ZONE VALVES. Install unit as described in this manual.
Ignition Sequence not activated when burner light is on (Fan is on and Fenwal not flashing) continued Stack Safety Limit Trips (Automatic Reset) Located on the front of the flue box. This device protects the integrity of the plastic venting material. If the temperature of the flue gases exceeds 225°F, 107°C, the limit will cut power to the control. Blocked internal tubes can increase the stack temperature to an unacceptable level. Flush out the boiler.
Two Flashes on Fenwal The Fenwal controller thinks that there is a flame prior to ignition. If the combustion sequence is normal, and there is no flame prior to ignition, the Fenwal control is defective, and must be replaced.
Three Flashes on Fenwal Indicates Ignition Lockout. If the condensate drain gets blocked, the boiler will become flooded, and terminate operation, as the flame rod becomes immersed. This will damage the flame probe. To correct, free the drain blockage, and permanently prevent it from reoccurring. Remove and dry off the probe. Reinstall the probe and try for ignition, if it fails to ignite, leave the fan run for up to three hours to dry out the insulation and probe.
Reset Boiler so it will attempt to ignite. Check for proper operation of ignition components. Make sure igniter glows and gas valve opens.
Check for proper line pressure at gas valve when it opens.
If boiler lights check for flame signal between FC1 And FC2 on Fenwal control. If lower then 1.2 micro amps see Boiler will not stay lit below.
Check combustion properties.
Boiler will not stay lit. Indicates lack of a good flame signal. In order to stay running the flame signal must be at least 0.7 micro Amps. If the Burner light on the Sentry is going out, go to “Burner shutting off”.
Check condensate drain for blockage and check the inlet piping for ingested snow or water (if the flame rod gets wet, it may need to be replaced). Check for resistance from flame rod to ground, must be an open circuit (O.L).
Check for proper polarity of line and neutral wiring to the boiler.
Boiler bangs or hisses Bangs or sounds like a kettle while burner is running indicating insufficient flow. Ensure the plumbing is as shown in manual. Check to see if pumps are faulty or end switches are stuck. This problem can lead to boiler overheating!
Sentry Controller Locks-up Excessive noise, current, or voltage spikes in the 120V power supply. Check for voltage at the wires going to the A-C-T terminals of the Boiler.
Check the magnitude of the line voltage power supply.
Check the Amp draw of output C1 and Ap (max 3 Amp).
Check the Amp draw of control on start-up (max 6 Amps)
Contact Hydrotherm.
Display Goes Blank No power to control or control failure. Check for 120V between terminals L1 and L2 at Sentry.
If 120V exists turn power off and remove line voltage harness from Sentry. Then check for resistance between L1 and L2 of control, if the circuit is open (O.L) the internal fuse has blown. Check for shorts in wires leading to circulators prior to replacing controller.
If 120V not present, check wiring and for 120V at source.
Boiler Lights rough or pulsates Typically an imbalance in the air to gas ratio. Ensure that the venting lengths are in compliance with the venting sections above.
Ensure that the line pressure during operation does not drop more than 20% from the static line pressure.
Momentarily remove the intake vent from the boiler during ignition, if unit lights smoothly with intake vent disconnected reconnect and check for proper combustion if unit maintains smooth operation after ignition. Calibrate for proper combustion. If problem persists contact Hydrotherm.
Fan appears to be creating a noise in the housing Slight vibration can cause noise in the residence. This is not a warranty issue. Use flexible gas line to insolate the vibration noises between the gas valve and the line.
Don’t hang gas lines from floor joists. Use rubber insulators with gas line supports.
Making a rubbing noise. This is not a warranty issue. If gas valve is not held when the gas nipple is connected, the force of tightening the fitting can damage the valve, and warp the fan housing.
If pipe is used, the gas line must not create any forces to the valve, either vertically (weight of line), or horizontally (misaligned connection)

HydroTherm HeatNet KN2 boilers troubleshooting

Situtation Suggested procedure
Nothing happens when the power switch is turned on. Check 120VAC power to connection board. Verify power is connected per wiring diagrams.
The Power switch light (ON -Position) should illuminate if power is wired correctly.
If the Ignition Control is active, but the front panel display is inactive check:
1. Cable and cable polarity from the control board to the display.
2. Check for 120vac on the primary of the transformer and 24vac on the secondary. If one of the 24vac interlocks has been shorted to ground or the 24vac output is low, the transformer may be damaged or a 24vac circuit may be miswired.
The KN control is equipped with resettable fuses on the power input circuit. Wiring power incorrecdy to die unit will cause these fuses to open. Once the incorrect wiring is corrected, the fuses should reset themselves in less than 5 minutes.
The display shows combustion air damper failure. lfyou are not using die combustion air damper dien it needs to be disabled in die AUX FUNCTIONS menu.
Hie prove switch for the combustion air damper is not closing. Check to make sure the dampers are being controlled by the output relay you specified when programming for the damper. Also check to make sure the prove switch is working properly.
If there is no proving switch, you must put a juniper wire across input connection (USER INTRLK).
If these steps have been done and you continue to get the error message, check the sensor TYPE specified in the SENSORS menu. If it is set to NONE, the controller will not recognize the closed circuit. Set the Sensor type to ON/OFF.
The display is displaying random characters or the control keeps resetting. There may exist a grounding problem with the controller or one of the boilers, pumps, contactors or other devices connected to it.
If all grounding is correct, there may be an issue with radiated or induced electrical noise (interference). This may be caused by arcing across a contactor’s contacts when starting a pump motor ora large electrical load. It may also be caused by the ignition transformer being improperly grounded or the spark gap being out of adjustment.
Attempt to identify the noise source:
1. What is the boiler/controller trying to do at the time of the failure?
2. Is the boiler on the same circuit as the noise source? (The boiler should have isolated power.)
3. Are shielded sensor wires used? (Ensure the shields are grounded only at the boiler control end.)
4. Are any sensors or sensor wires located near a transmitting antenna? (Move sensor)
There are no heating boilers on. Check the settings for OA SETPOINT and OA RESET.
1. If the outdoor air temperature is above the OA SETPOINT and OA RESET is on, the circulator pump relay will be locked out and the heating boilers will not fire.
2. It the w’ater temperature is within the heating band around the setpoint, boilers will not come on.
3. Ihe water temperature must fall below’ the lower band limit to begin firing boilers.
Unable to change the # of Boilers in the BOILERS menu. In H-Net method, the KN control auto-detects the boilers in the system and adjusts the number of boilers accordingly.
Using H-NET, if the numbere of boilers is not being detected properly as the actual number of boilers in the system, check each boiler. There can only be (1) master boiler, but there can be up to 15 member boilers.
Make sure only the master boiler has a Header Sensor connected.
Verify that each boiler’s HeatNet cable is in place.
Verify that each boiler has a unique address assigned (ADVANCED SETUP D1STRIB CTRL, LOCAL AD).
The BOILERS menu only indicates one boiler, but there are member boilers connected. The amber light blinks on all of the boilers communication’s jacks. Verify that the latest version of firmware is installed on all boilers.
All boilers in a system must have the same firmware revision (version).
Verify the proper termination is set on the Master and the last Member boiler.

HydroTherm KN SERIES boilers troubleshooting

The “Power On” light doesn’t illuminate. Ensure that proper voltage is being supplied to the unit Inspect the circuit breaker for the boiler circuit Check the light
Ensure that the power switch operates properly and is wired correctly
Lockout water limit is displayed with a call for heat. Check both the high limit and low water cut off.
Ensure that the boiler has been completely purged of air.
Ensure that all system valves are in the correct position.
Lockout gas pressure is displayed with a call for heat. Ensure that the manual main gas valve is open. Ensure that there is sufficient gas pressure supplying the boiler.
Check pressure setting on the low gas pressure switch.
Lockout flow switch is displayed with a call for heat. Ensure that there is sufficient water flow through the boiler
UV scanner switch is displayed flashing along with the normal running display. Ensure the scanner-cooling pump is operating.
Make sure there are no obstructions in the tubing supplying the air to the scanner.

HydroTherm VGX 88 boilers troubleshooting

Problem Possible Cause Suggested Remedy
Pilot Outage Defective Thermocouple Replace
Heavy Draft Blowing across Pilot Redirect Air Movement or Eliminate
Plugged Pilot Orifice Replace Orifice
No Gas Check Manual Pilot Valve Check Main Gas Shut-Off Valve Check Manual Meter Valve Consult Gas Company
Defective Thermopilot Switch Replace
Defective Ignition Control
Main Gas Valve Will Not Open (Spark Ignited Pilot) No Power Check tower Source with Meter Check Fuses
Defective Gas Valve Replace
Low Water Level in Boiler or System Causing Low Water Cut-off to Function Check for Leaks Check Feeder (if Supplied)
Defective Ignition Control Replace
High Gas Pressure Switch Open (if Provided) Check Switch Setting Check Manifold Gas Pressure
Low Gas Pressure Switch Open (if Provided)
Main Gas Valve Will Not Open (Standing Pilot) No Power Check tower Source with Meter Check Fuses
Defective Gas Valve Replace
Pilot Out Relight Pilot (May have defective pilot valve or relay)
Low Water in Boiler or System Causing Low Water Cut-off to Function Check for Leaks Check Feeder (if Supplied)
Defective Thermopilot Switch Replace
Defective Thermocouple Replace
High Gas Pressure Switch Open (if Provided) Check Switch Setting Check Manifold Gas Pressure
Low Gas Pressure Switch Open (if Provided) Check Switch Setting Check Inlet Gas Pressure
Burner(s) Burning wilh Yellow Flame Air Adjustment Screws Turned in Too Far Adjust Screws Out
1 ow Gas PnvKi ire in Manifold (Insufficient Air Injection) Adjust Main Gas Pressure Regulator or Check Line Pressure
Burner torts Partially Closed (Rust, Dirt. Lint, etc) Replace Burners or Clean Ports
Insufficient Air for Combustion Check Size of Combustion Air Openings to Room If Undersized, Correct as Required Check for Negative Pressure in Boiler Room
Oversized Burner Orifice Install Correct Orifice
High Gas Pressure in Manifold Adjust Main Gas Pressure Regulator
Gas Spillage from Draft Hood Relief Opening Insufficient Draft – Chimney Too Low Increase Height or Add Induced Draft Fan
Insufficient Draft – Chimney Too Small Replace Chimney or Add Induced Draft Fan
Insufficient Draft – Blockage in Chimney or Vent Repair Chimney or Vent
Insufficient Draft – Downdraft Caused by Chimney Location with Respect to Other Buildings, Roofs, etc. Install Chimney Cap
Negative Pressure in Boiler Room (Due to Exhaust Fan or Duct System) Remove Exhaust Fan or Isolate Fan From Boiler Room
Insufficient Combustion Air Openings Provide Correctly Sized Combustion and Ventilation Air Openings
Main Gas Valve Opens But No Gas Flows Manual Valve Closed at Gas Train Open Valve
Manual Valve Closed at Meter
Test Firing Valve Closed (if Provided)
Water Hammer On Start-Up Sags in Steam Piping or not enough Pitch Correct Piping Condition
Concentric reducers causing condensate pooling Correct Piping
Drip trap failed closed Replace Trap or Trap Element
Dry returns wetted due to new boiler water line higher than old boiler Correct Piping or Install Feed System and Traps
No drip line on the back side of a back-pitched motorized valve Install Drip Line and Trap