Forced Hot Water Heating Systems:
Forced hot water heating systems have supply and return plumbing lines to carry the heated water. They have supply lines that bring the heated water to the radiators in each room. They have return lines to bring the water back to the boiler, after it has given off its heat, to be reheated and recirculated.
There should be at least one radiator in each room. The radiators should be located underneath a window of an exterior wall. This will provide the maximum efficiency since the warm air will mix with any cool, drafty air that comes in through the cracks of the window frames. Radiators need to be bled about once per year. When a contractor "bleeds" a radiator, they merely open a small valve on the radiator to allow trapped air to escape. This leaves space for hot water to heat the radiator efficiently. Sometimes you'll find that only a few radiators don't get warm during your heating system test. Usually this is because the radiators need to be bled or the handle valve is turned off. Either of these conditions can be easily corrected.
Separate heating zones are established by circulator pumps or zone valves on the return pipes. The pumps or valves open and close the circulation of hot water. Circulator pumps look like a round attachment located on the return line of the boiler. When the circulator pump isn't running, the water is blocked by the pump. As a result, no water can pass through the lines to the boiler to be circulated. Zone valves are small attachments with wires leading to them on the return lines before they reach the circulator pump. When the zone valve is shut, no water can pass through that zone, even if the circulator pump is running.
One type of zone installation has a circulator pump on the return line in the back of the boiler. Then there are separate zone valves on the return lines before they reach the circulator pump. Another type of zone installation is to have a separate circulator pump for each zone return line leading back to the boiler.
Circulator pumps need just a drop of oil in the oil ports maybe once a year. Tell the client to have the service contractor check this with the tune ups. If the circulator pump is operating properly then you'll be able to see the bearings spinning in the visible areas. Also, the return line will begin to get warm.
Sometimes an aqua stat controls the circulator pump. This will keep the circulator turned off until the water gets warm enough in the boiler. The purpose of this is to prevent cold water from being sent to the radiators. After the house thermostat shuts off the burner, the circulator will usually keep running. Since there's is hot water in the boiler, the circulator still runs for energy efficiency.
If you're inspecting a very old house, you may come across a gravity hot water heating system. As I noted earlier, it's very rare to find a gravity heating system. A gravity hot water system will have most of the same components as a forced hot water system. However, there won't be a circulator pump to push the heated water through the house. Circulator pumps weren't used years ago because hot water rises on its own. The water pipes for a gravity system had to be much wider to allow easy passage of the hot water. Once again, the problem with a gravity heating system is that it takes too long to warm the house since the water movement is so slow. Most of these systems have been updated to forced hot water heat due to the increased energy efficiency of using a circulator. If you ever find a gravity heating system, tell the client to have it updated.
Check all heating pipe joints and the circulator for rust or leaking conditions that'll require repairs. You'll usually find some rust unless it's a new unit. Open any panels on the heating system that don't require tools. You should be able to view the heat exchanger and the firebox. Some units are sealed systems that require tools or can't be opened. Tell the client that you're limited due to the sealed system.
Check the heat exchanger for any rust or leaking conditions. Check the condition of the firebox where the burner flame is. Often the firebrick in an oil fired unit will be deteriorated from the long exposure to the heat of the burner. A new lining can usually be installed in the firebox without a major expense.
Check for a water pressure reducing valve for hot water systems. This is a small valve that looks like a miniature bell. It's located on the water line that brings water to the boiler from the plumbing system. This reduces the water pressure that's coming from the house plumbing lines. The pressure in the house plumbing lines is usually about 30 to 60 psi (pounds per square inch). The water pressure reducing valve will lower the water pressure down to about 12 to 15 psi before it enters the boiler. I'll explain the reason for reducing the water pressure in a minute.
For hot water systems, there should be a backflow preventer next to the water pressure reducing valve. This prevents water that has entered the boiler from recirculating backwards into the house plumbing lines. The purpose is to prevent the unsanitary boiler water from mixing with the faucet and shower water supply for the rest of the house.
Sometimes your client will ask you, "Do I have to add water to the boiler during the heating season?" You don't have to add water to a forced hot water heating system because the boiler water supply valve is always open. Therefore, water enters the system on it's own whenever necessary. For safety, there should be a low water cutoff switch on the boiler in case the water level drops too low. These devices will automatically turn off the boiler when the water level gets too low for proper operation of the heating system. If someone closes the water supply valve or there is a problem with the pipes, you don't want the boiler to become empty. This can be a dangerous condition if the burner turns on because there won't be anything to transfer the heat to.
Check for an expansion tank on the boiler room ceiling for hot water systems. This is a metal tank that allows the heated water to expand. When you heat water, it expands. When water freezes it expands as well. The heated water needs a cushion to expand or else it'll burst some pipe joints. Also, heated water that doesn't have a cushion will discharge the pressure relief valve to relieve the pressure. The expansion tank has an air pocket or a rubber bag inside it. This cushions the water as it expands so the pressure in the system doesn't get too high. Expansion tanks need to be checked periodically for water logging problems. They should have a bleeder valve to put air in it if the tank becomes waterlogged. Check for a drainage valve on the bottom. These valves should be drained at least once a year to remove any rust and sediment that build up in the tank.
Check for a properly operating pressure gauge. The gauge should move while the boiler is being tested. You should tap all pressure gauges with your finger before viewing them to take a reading. Many times you'll find that the needle inside of these gauges will stick. You should also tap the gauges while checking the pressure during any testing to make sure the needle is moving properly. The proper operating pressure for a hot water heating system is 12-22 pounds per square inch. Make sure the pressure doesn't go too high and record the readings you get. There may also be a water temperature gauge in the pressure gauge. Monitor this temperature periodically during the test and record the reading.
Check for a pressure relief valve on the boiler. This is a safety device that helps prevent the heating system from becoming dangerously high in pressure. If the pressure reaches 30 psi, then the valve will discharge to relieve the system so the boiler won't explode. This is why the water pressure reducing valve has to lower the house water pressure before it enters the heating system lines. It lowers the water pressure so the pressure relief valve won't discharge right away. Let's say the water entered the boiler at the normal house water pressure of 30 to 60 psi. Then the pressure relief valve would discharge, without even turning on the heating system.
The pressure relief valve must be located directly on the boiler unit for proper operation. It must be piped to within eight inches of the floor to prevent scalding anyone when the valve discharges.
The pressure relief valve must not be rusty and must be located directly on the boiler for proper operation. It must be piped to within eight inches of the floor to prevent scalding anyone when the valve discharges. When water or steam discharges from this valve, then there's a problem and a heating repairman has to check out the system. Sometimes you will find a hose attached to the relief valve leading into a sink or drain. This is not recommended for any pressure relief valves. The reason is that the homeowner must know that the valve is discharging so they can see there is a problem condition. If the valve drains into a sink, the homeowner might not be aware of any problems that need repairs.
There should be a drain valve on the lower part of the boiler. It's usually in the rear and looks like a water faucet bib. This valve is used to drain about a half gallon of water into a bucket each month. This removes the rust and sediment that normally build up in the system. It's similar to the necessity of changing the air filters on FH Air heating systems or on air-conditioning systems. Drain a small amount of water into a bucket to determine the color and see if the system has been maintained and properly drained monthly. If the water that comes out is very dirty, then the heating system has not been maintained properly and this will cut down its life expectancy. If the water that comes out is clean, then the heating system probably has been maintained properly and this will increase its life expectancy.