When inspecting a hot-water heating system, you should first determine whether it is a gravity or forced system. Sometimes an open expansion tank is found in the attic during the interior inspection. This would normally indicate a gravity system. Often, however, the expansion tank is no longer functional and was replaced by a closed expansion tank when the system was converted to forced circulation. You can easily tell whether a system has forced or gravity circulation by checking the equipment associated with the boiler. A forced system will have a circulating pump in the return line near the boiler. Record the type of system on your worksheet.
Next, look at the pressure gauge and record the operating pressure. The normal operating pressure should be between 12 and 22 psi. Since the water-makeup valve (pressure-reducing valve) is set to introduce water into the system when the pressure drops below 12 psi, any pressure below that value indicates either a malfunctioning valve or the need for adjustment. A low-pressure reading is fairly common.
If the pressure gauge indicates an operating pressure of 30 psi, the relief valve should be discharging. Sometimes the relief valve has already discharged and lowered the pressure to about 28 psi. In this case, the exposed end of the relief valve will have water dripping from it, and there will be a pool of water on the floor. A high-pressure condition that results in the relief valve discharging will usually be caused by a waterlogged or undersized expansion tank. If domestic hot water is generated through the heating system, another possible cause for a high-pressure condition is pinholes in the coils of the water heater. Regardless of the cause of the high pressure, the condition must be corrected.
Locate the relief valve. From a safety point of view, it should be boiler-mounted. If there is no boiler-mounted relief valve (and often there is not), the installation of one should be considered. Do not check the valve to determine whether it is operational. Bits of corroded material, sediment, or mineral deposits may prevent the valve from reseating properly and shutting off. Your best bet is to check the valve after you move into the house. At that time, if it does not reseat properly, it should be replaced. A relief valve is inexpensive. These valves should be checked at least once a year by pulling the lever and allowing a small quantity of water to flow. This action flushes any sediment that tends to build up before it has a chance to clog the valve. Some relief valves do not have levers for testing the unit. If you have such a relief valve on your boiler, you should consider replacing it.
As the various zones are being checked, inspect the zone valves for dripping water and deposits. Even though the valves might be working during your inspection, if water is dripping from the valves, they should be replaced. The dripping water results in a mineral-deposit buildup that can eventually cause the valve to "freeze" in an open or closed position. This might happen, and usually does, on the coldest night of the year. Zone valves are perhaps the weakest link in the heating system, and their occasional replacement should be anticipated.
Is the circulating pump operating properly? Just because you can hear the pump operating or feel its vibration does not mean that it is functioning properly. The coupler between the pump and the motor may be broken, and the noise that you hear or the vibration that you feel may be only the motor turning, not the pump. You can be sure the pump is operating by putting your hand on the return pipe associated with that pump. After a while, the pipe will get hot if the pump is operational. Check the gasket between the pump and the motor for signs of current or past leakage. This is a vulnerable joint for leakage.
Is the circulating pump emitting any unusual or loud sounds? If it is, the noises might indicate faulty bearings, and the condition should be checked by a service organization. If you see smoke coming from the circulating pump or smell electrical insulation burning, the entire system must be shut down immediately and the condition corrected. One last check of the circulating pump is to determine whether it operates continuously or intermittently. If the circulating pump continues to run long after the thermostat is not calling for heat, it is in continuous-mode operation. This mode, discussed in chapter 14, can be modified to an intermittent operation.
If the heating system is used for generating domestic hot water, the thermostat will not control the burner, only the circulating pump. In this case, check the temperature of the boiler water (look at the temperature gauge). If the temperature drops below 150° F and the burner does not fire, it will indicate a faulty or improperly set aquastat. In most cases, the burner will be activated when the temperature drops below 180° F.
In addition to the above, with high-efficiency condensing and pulse boilers, look at the piping associated with the inlet air supply, exhaust gas vent, and condensate drain. Check to see that there are no loose sections, that there is no blockage at the pipe terminations, that the exhaust pipe is not combined with the exhaust from the water heater, and that the horizontal portions of the exhaust pipe slope back to the boiler. Also check that the condensate pipe discharges into a floor drain or condensate pump rather than a hole in the floor slab.
In this system, a water line showing the level of water in the boiler should be visible in the level gauge. Look for the gauge. If it is dirty, it must be cleaned. A gauge that is completely filled with water indicates too much water in the system, and an empty gauge indicates an insufficient amount of water in the boiler. When the water level in the gauge is unsteady (rising and dropping), it indicates a problem condition that might reflect an excessive grease and dirt buildup in the boiler or that the boiler is operating at an excessive output. In either case, it should be corrected.
Check the heating unit to determine whether it has all the required safety controls. A steam system should have a low-water cutoff, a high-pressure limit switch, and a relief valve. If any of these items are missing, record the fact on your worksheet. Look for the low-water cutoff. Is it the built-in type or externally mounted? If it is externally mounted, you should test its operation. This is a normal procedure that the manufacturer recommends the homeowner perform periodically. If the relief valve is old, then as a precautionary measure it should be replaced after you take possession of the house.
Look for the condensate return line to the boiler. Is it a wet or dry return? If it is a wet return, it should be connected to the boiler by means of a special piping arrangement, a Hartford loop. Is there one? If not, the installation of a loop should be considered.
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