Gas Fired Boiler Repair

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Introduction to the Hot Water Boiler

Gas Fired Boiler

Gas Fired Hot Water Boiler
A hot water boiler is an appliance used to heat water for a hydronic heating system.  The hot water is distributed through the home in pipes and radiate heat into the rooms with either a steel radiator (newer homes) or cast iron radiator (older homes) or baseboard convectors or "fin-tube" (newer homes). Once the radiator or baseboard fin-tube convector is heated with the hot water, the water is returned back to the boiler to be re-heated and the water circulation loop continues. In addition to radiators, the hot water boiler is also used with radiant floor heating systems.These boilers can be fueled either with natural gas or propane (gas-fired) or they can burn fuel-oil (oil-fired).  Fuel-oil boilers are higher maintenance than their gas burning counterparts and require regular attention to the blower and oil filter.

Boiler Components

Main Components of a Gas Fired Boiler

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Components of a Hot Water Boiler
The boiler is more complex than a forced air furnace in that it has more parts, valves and controls.  However gas-fired boilers are fairly reliable and most problems, when they do occur, usually relate to the expansion tank or water circulator pump(s).Let's take a quick look at the major components of the boiler for a forced-water (hydronic) system:
Hot Water Supply Side:
Aquastat - The thermostat that regulates the boiler's temperature
Gas Valve and Burners - Combustion assembly that heats the water chamber
Combination Pressure / Temperature Gage (Tridicator) - Monitors water temperature and pressure
Water Feed Valve - Controls water flow to boiler
Pressure Reducing Valve - Automatically maintains correct water pressure at about 12-15 psi
Air Vent - Automatically purges unwanted air from hydronic system
Expansion Tank - Critical component that allows expansion of water as it heats. There are two types of expansion tanks, the older larger style horizontal steel expansion tank and the newer smaller style diaphragm expansion tank.
Flow Control Valve - Regulates flow of hot water to system
Pressure Relief Valve - Relieves high water pressure
Hot Water Return Side:
Circulator - Electric pump that circulates water through the system
Drain Valve - Valve that opens to allow draining the boiler.

PROBLEM: Boiler Produces No Heat

Electronic Ignition (Intermittent Pilot)

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PROBLEM: Boiler Produces No Heat
Possible Causes

• Boiler has no power
• Water level is low
• Pilot or electronic burner ignition malfunction
• Thermostat malfunction
  

Possible Repairs

• Circuit breaker or fuse controlling the furnace is tripped or blown. Reset tripped circuit breaker.  Replace blown fuse.
• Maintain water level at half full. The boiler's automatic filling system using the pressure relief valve should maintain proper water level by maintaining a 12-15 psi pressure.  If you do not have a pressure reducing valve you can also manually feed the boiler by oping up the water feed valve until boiler pressure reaches 12 psi.
• Natural gas or propane control valve to boiler burner is closed.
• Pilot light is out.  Relight standing pilot.
• Troubleshoot electronic ignition system if boiler has no standing pilot.
• Check that thermostat is in heat mode and has appropriate temperature setting.
• Try moving thermostat setting for temperature up or down a few degrees.
• Troubleshoot thermostat.
  

PROBLEM: Poor Heating Performance

Boiler Tridicator (combo temperature / pressure gage)

PROBLEM: Poor Heating Performance
Possible Causes

• Sudden Change: Improper water level
• Gradual Change: Mineral deposits in boiler and heat exchanger
  

Possible Repairs

• Check reading of the Tridicator (combination pressure / temperature gage). If water pressure is low (below 12 psi) the system needs to have water added. The boiler's automatic filling system using the pressure relief valve should maintain proper water level by maintaining a 12-15 psi pressure.  If you do not have a pressure reducing valve you can also manually feed the boiler by opening up the water feed valve until boiler pressure reaches 12 psi.
• If problem arose gradually then the cause may be due to deposits in the system. Flush the boiler or call a service technician for this task.
• Expansion tank may have too much or too little water.  It must be properly charged with air to prevent boiling. See the next section for more detailed review of the expansion tank.
  

PROBLEM: Expansion Tank Has Excess Water and Inadequate Air

Amtrol Diaphragm Style Boiler Expansion Tank

© Amtrol 2007

PROBLEM: Expansion Tank Has Excess Water and Inadequate Air
There are two basic types of hot water boiler expansion tanks. There is the older style large horizontal steel tank and the newer style smaller diaphragm tank (shown in photo above).
In older boiler systems the steel expansion tank may be found in the attic or suspended between joists in the basement. In newer systems the diaphragm expansion tank may be attached to the boiler piping near the boiler.  The expansion tank must be properly charged with air to prevent water in the system from boiling and exceeding the desired 12 psi of pressure.
For tips on how to drain these two tank types, please see the tutorial How to Re-charge a Hot Water Boiler Expansion Tank.

PROBLEM: Water Leakage Around Boiler

Boiler Pressure Relief Valve

PROBLEM: Water Leakage Around Boiler
Possible Causes

• Faulty circulator (pump)
• Faulty pressure relief valve
• Leaking water pipe connection
  

Possible Repairs

• Most repairs to the circulator will require a service technician.
• If the circulator is leaking replace the pump seal.
• If the pressure relief valve is leaking, the system expansion tank may be filled with water. See previous section PROBLEM: Expansion Tank Has Excess Water and Inadequate Air.
• If pressure relief valve is leaking and the problem is not the expansion tank, the valve may have sediment preventing it from closing.To check this turn the boiler off and let it cool.  Lift the manual pressure relief lever and discharge some water for a 3 seconds, letting the lever snap back into a closed position. The water should discharge strongly and be relatively clean. If the valve leaks slightly afterward this could be caused by sediment trapped in the seat causing small leakage.  Open the valve again and discharge a second time.
• If the pressure relief valve will not close at all, close the boiler water feed valve and remove and replace the relief valve.
• If no water discharges from the pressure relief valve at all, the valve is plugged and needs to be replaced or there is no water in the boiler.
• If water is leaking or dripping from a pipe. follow the leak back to its source and repair the connection where the leak is originating.  This will require turning off the water supply to the house and draining the boiler system.
  

PROBLEM: Not All Radiators Heat

Hot Water Radiator Bleed Valve

PROBLEM: Not All Radiators Heat
Possible Causes

• Trapped air in line
• Trapped air in radiator (top is cooler than bottom)
• Faulty zone valve or circulator
  

Possible Repairs

• Bleed air from cool radiator by opening radiator bleed valve at top of radiator. When water squirts from radiator, close valve.
• Check circulator for proper operation (motor runs). There may be dedicated circulators for different heating zones in the home.
• Check zone vale for proper operation. Water pipe should be hot up to and beyond the zone valve. If the valve is bad or stuck, it will be hot up to the valve but cool off slightly beyond the valve.
  

PROBLEM: Noisy Pipes

Hot Water Boiler Circulator

PROBLEM: Noisy Pipes
Possible Causes

• Faulty circulator
• Water trapped in return lines
  

Possible Repairs

• Check the circulator. There is a spring loaded coupling that connects the pump to the motor. When it breaks after the pump jams, the coupling will make a loud noise as the motor runs.
• Check that the pitch of the return lines slope back toward the boiler. Adjust pitch with new pipe hangers if necessary.
• Adjust pitch of radiator with a shim so that it slopes back toward the return pipe.