How to Diagnose Problems with a Hot Water Heating System

Ask This Old House plumbing and heating expert Richard Trethewey helps a homeowner figure out why one of her radiators is not working.

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Richard identified that the 1950s era home he visited was piped with a diverter tee setup, where a single, combined supply and return line runs from the boiler.In part of Richard’s explanation on the radiator, he explained the diverter tee in the dual piping to each radiator. The diverter tee slow-stems the flow of water at one end, increasing the back pressure and forcing the water through the first pipe and into the radiator.

Time: varies
Cost: varies
Skill Level: Difficult

Steps:
1. Richard goes over some of the places to check when adequate heat is not being delivered from a forced hot water heating system.
2. In this home, which means the water heats up in the boiler, goes up through the pipes, through the radiators, gives off heat to the room, and falls back down to the boiler to be heated again. That process is helped via an electric circulator pump which can be tested to ensure it is working properly.
3. With any forced hot water system, there must be the right amount of water pressure going into the boiler and to the pipes. To help that, a pressure reducing valve lessens the amount of water pressure from the city to the boiler. The pressure reducing valve can be tested and a pressure gauge on the boiler will also indicate system pressure.
4. An expansion tank to reduces the stress on the system. The top portion is filled with water and the bottom air under pressure. In between the two, is a neoprene diaphragm to act as a shock absorber to the pressure. If that diaphragm fails, it can cause problems with the system.
5. If only one radiator is failing to give off heat, check the air valve to determine if there is any excess air in the system.
6. Check the shut off valve going in to the radiator, which may have been turned off for service or an attempt at zoning.

Richard showed 3/4-inch copper monoflo tees. Those can be found at local home centers or plumbing supply stores.

After diagnosing a hand valve that was inadvertently turned off, Richard used the Flir One infrared camera attachment for a smart phone manufactured by Flir [www.flir.com/] to confirm that heat was reaching all parts of the radiator.

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How to Diagnose Problems with a Hot Water Heating System | Ask This Old House
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