Gas Boiler Repairs

There are any number of things that can go wrong with a gas boiler. Here we identify some of them and, where possible, offer solutions.

With all issues involving gas boilers, if you are in any doubt contact a registered gas engineer. A gas-fired hot water boiler has many parts, valves and controls, but for the most part they are fairly reliable and when they do have problems, these usually relate to the expansion tank or water circulator pump(s).

Three common problems with gas boilers

Problem 1 – Boiler produces no heat

Possible causes include: no power; a low water level; a malfunction with the pilot light or electronic burner ignition; or a thermostat malfunction.

Possible repairs:

  • If the circuit breaker or fuse controlling the furnace is tripped or blown reset the tripped circuit breaker and/or replace the blown fuse. 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.
  • Relight pilot light.
  • Move thermostat setting for temperature up and down a few degrees.

Problem 2 – Poor heating performance

A sudden change in performance might be due to incorrect water levels, a more gradual change might be related to mineral deposits in the boiler and heat exchanger.

Possible repairs:

Check the combination pressure / temperature gage, and if the 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.

If you feel the problem might be mineral deposits in the boiler, flush the system or call a service technician to do this task.

Problem 3 – Expansion tank has excessive 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. 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.

Some of the signs that you have a problem with your expansion tank include: water spurting from the pressure relief valve on the boiler; an abnormally high pressure reading on the gauge (above 20 psi), and the tank is hot to the touch from bottom to top.

Any of these symptons suggest that there is too little air and too much water in the expansion tank.

Possible repairs:

If the bottom of the tank doesn’t feel hotter than the top it must be bled or drained of excess water. To do this, turn off the boiler, close the water shut-off valve and let the tank and system cool. The expansion tank combination valve will release water and let in air. Attach a hose to the combination valve and drain about three gallons of water. If there is no combination valve on an older tank, then shut off the valve between tank and boiler and totally drain expansion tank. Open the water supply valves and let the system fill back up. Turn the boiler back on and let it recharge. Let the system run for 1-2 hours and then recheck it.

By recognising problems and knowing how to deal with some of the common issues, you can save a lot of money on call-out charges.