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.
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 pumps.
Let's take a quick look at the major components of the boiler for a forced-water (hydronic) system:
Hot Water Supply Side:
Hot Water Return Side:
- Boiler has no power
- Water level is low
- Pilot or electronic burner ignition malfunction
- Thermostat malfunction
- 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.
- Sudden Change: Improper water level
- Gradual Change: Mineral deposits in boiler and heat exchanger
- 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.
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.
- Faulty circulator (pump)
- Faulty pressure relief valve
- Leaking water pipe connection
- 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.
- 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.
- Trapped air in line
- Trapped air in radiator (top is cooler than bottom)
- Faulty zone valve or circulator
- 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
- Faulty circulator
- Water trapped in return lines
- 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.