Tip & How-To about Heating & Cooling

Valve Pressure Reducing or Pressure Reducing Valve

The pressure reducing valve on a boiler is the way that the water pressure in the boiler is controlled. The standard pressure for many hot water boilers is considered to be 12 PSI. To keep the boiler pressure at or near the 12 PSI mark a small valve is used for pressure reducing. Most domestic water systems run between 20 and 60 PSI, so the pressure must be reduced for the boiler.

This pressure reducing valve is installed in the pipe that goes from the domestic cold water to somewhere in the piping on the heating system, usually at or near the expansion tank. The valve is mostly maintenance free but will create some problems at times. Some of the things that can go wrong are:

  1. The valve seat can get dirt stuck under it causing water to leak by and increase the pressure in the boiler, causing the relief valve to release water periodically.
  2. The valve can become plugged with dirt causing the boiler to not have enough water pressure, which will cause circulation problems with the boiler pumps.
  3. The valve can leak causing a mess around the boiler area.

Replacement of the pressure reducing valve is not difficult if the installer strategically placed manual valves so that the reducing valve can be isolated from the rest of the system for replacement.
If the water pressure reducing valve fails in any way, it is usually best to just replace the whole valve rather than trying to repair or fix it. I have tried a number of times with only temporary results. These valves are not a high dollar item and the time it takes to fix them is not worth it.

http://www.fixya.com/support/r3696173-expansion_water_tank_boiler_expansion

http://www.fixya.com/support/r3705970-heating_circulating_water_pump_problems

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2 Answers

why can't i fill my boiler


You didn't specify what kind of boiler you have. Some low pressure steam boilers have a manual fill valve as well as an automatic float switch valve. Hot water boilers have a pressure reducing valve that constantly monitor the boiler pressure and maintain 12 to 18 PSI for the safety of the boiler. If the boiler runs out of water there is a good chance it will rupture and become unrepairable. If you are saying your boiler won't fill, and its a hot water boiler, the pressure reducing valve is probably blocked with sediment and needs replacement. The valve is in the water line that feeds directly into the boiler return line from city water. Hope this helps.

Oct 01, 2014 | Water Heaters

1 Answer

What is the normal PSI of the operating system?


As with any hot water or heating appliance, a hot water boiler system requires a constant pressure flow to maintain the optimum temperature. Hot water boiler systems are equipped with a pressure gauge and an automatic pressure reducing valve that will add water to the system if the pressure drops. Despite the pressure reducing valve, owners should be familiar with the standard PSI of their hot water boiler system and should check the pressure reading regularly.
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Sep 29, 2014 | Cars & Trucks

1 Answer

Hi! My hot water taps from the wash hand basin and mixer bath has low pressure. I`ve got a combi boiler in the first floor. Can I install a single impeller pump connected from the hot water outlet from the boiler to the pump`s inlet and them from the pump`s outlet tothe hot water tap?


In a word no. Combi boilers work on balanced pressure.ie the mains cold supply to the boiler should be around 1 bar minimum which would give a hot water pressure of the same 1 bar. Assuming the cold water pressure is fine, it sounds like you have a restricted flow on the hot side. If you live in an area with water problems the hot water systems pipework calcify over time effectively reducing water flow. Unless any flexi hoses are kinked, check if there are any filters in the appliances that may be blocked.Also check all valves are fully open and if possible check if there are any restrictions at the valves. Failing all that and the taps are in good order it is possible to fit a pump before the boiler but this may only be a temporary fix overall.

Apr 04, 2010 | Plumbing

1 Answer

how do you fill a slant fin boiler


The boiler should have a make-up water connection from the home cold water supply line. Depending on when it was installed it will have a back flow preventer in line before the pressure reducing valve. The pressure reducing valve is designed to fill the boiler if the water pressure in the boiler falls below a specific set point, usually 12-15 pounds. I will be piped to the return side of the boiler in most cases. If the boiler is not filling the PRV could be defective, or depending on the specific controls, there could be a low water float assembly, either electronic or mechanical that activates a control valve to fill the boiler and that may be either stuck or defective. Boilers should be properly maintained at a minimum of every other year, once a year is best to ensure that you get 25+ years of operation from them.

Sep 15, 2009 | Heating & Cooling

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