Water supply causing pressure relief valve to open

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Old 03-30-14, 08:37 AM
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Water supply causing pressure relief valve to open

Shut off main water supply to the house to fix a hose bib. When main water supply was turned back on the pressure relief valve on the hot water boiler opened. Boiler gauges read 30psi and 145 degrees F. I have to keep the water supply line to the boiler shut off in order to prevent discharge from pressure relief valve (rated at 30psi).
 
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Old 03-30-14, 08:46 AM
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Dave, start by reading these:

http://www.doityourself.com/forum/bo...sion-tank.html

http://www.doityourself.com/forum/bo...ure-gauge.html

Probably what happened is when the water supply was turned back on some 'crud' in the water line got into your pressure reducing valve for the boiler system.

Since you will be de-pressurizing the boiler (unless you have valves on BOTH sides of your pressure reducing valve to isolate it for service) to replace the reducing valve, it is also wise to service your expansion tank... let us know if you don't have the smaller type of tank mentioned in the thread and we can give instructions for servicing that.
 
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Old 03-30-14, 08:51 AM
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Dave,
You have an automatic feed valve on your cold water supply to the boiler that may be stuck open and letting water leak by.
They come preset at about 12 psi from the factory. If you have isolation valves before & after and if it can be removed you can try flushing it out or if defective replace it.

Good Luck,
 
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Old 03-30-14, 08:53 AM
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I have a back flow preventer between two valves on the water supply line. Does the backflow preventer also act as the pressure reduce?
 
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Old 03-30-14, 09:08 AM
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Does the backflow preventer also act as the pressure reduce?
No, only backflow prevention.

You may find that will be leaking too if it got crud in it. Water supply lines collect a lot more crud than we usually know about and when they are depressurized the stuff breaks loose. If you've ever watched when the water company flushes it's mains by opening fire hydrants you would know exactly what I mean... stuff comes out looking like mud sometimes!

You might also need to clean the aerators on all your sink faucets.

When you do replace the pressure reducing valve be sure to somehow flush that water line out at full blast for a few minutes to clear any remaining crud or you'll ruin the new valve.
 
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Old 03-30-14, 10:08 AM
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I have attached a couple of pictures to help explain. I have traced the water supply line back to the main supply for the house and there are two isolation valves and a backflow preventer (watts No. 9D). I'm not sure where the pressure reducing valve would be located.
 
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Old 03-30-14, 10:32 AM
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Dave, I don't see a pressure reducing valve in the pics, and your backflow preventer is installed upside down.

The reducing valve should be on the boiler side of the backflow preventer and unless it's hiding back behind the flue pipe, it doesn't appear that you have one.

They aren't an absolute necessity, but it does mean that the operator must do due diligence in monitoring the system pressure and add water manually as needed.

How long have you lived with the system?
 
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Old 03-30-14, 10:33 AM
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What is that device to the left of the boiler?
 
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Old 03-30-14, 10:37 AM
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The device (the black one) is a water softener. We have only lived here since Feb. Barely two months.
 
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Old 03-30-14, 11:25 AM
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We have only lived here since Feb. Barely two months.
OK, you need to know a few things then...

The MINIMUM pressure in the boiler should be 12-15 PSI when cold... ambient... room temp. Taller homes, above 2 stories, will need slightly higher minimum pressure.

Since you don't have a pressure reducing valve, you are responsible for monitoring that pressure and adding water as needed to maintain it. Theoretically, once the system is filled, you should never NEED to add water, but reality is that very few systems will hold pressure over long periods of time.

You should know that the gauge is accurate.

Also, you should perform the maintenance on the expansion tank since this is the component that prevents the pressure from going too high when the boiler fires and the water is heated and expands. That tank is where the expanded water goes.

OR, plan on adding a pressure reducing valve in the near future, and turn that backflow preventer over so the vent points DOWN.

I suspect that what happened when you turned the water back on is that you opened the manual feed valve to the boiler by accident...
 
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Old 03-30-14, 11:36 AM
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okay thanks. Now that summer is approaching I think I'll take the system down and add the pressure reducer, fix the backflow preventer, do maintenance on the expansion tank, and replace some of the old isolation valves.
 
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