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jeffcubsfan
Water Pressure Mystery

I can't figure this one out. When I turn on my shower/tub (single lever pull system), the pressure starts out great. Then, after 20 seconds or so, the pressure reduces by half. No other faucets have this issue. So I have already replaced the shower cartridge (didn't help), cleaned the shower/tub diverter (didn't help), and replaced my shower head (again, didn't help). I recently had my hot water heater replaced, but the pressure was fine for months afterwards. I also have a natural gas boiler/radiator heating system, but no water is being drawn to it. If anyone has thoughts on other possible causes and solutions, I would be very thankful.

HoustonRemodeler
Re: Water Pressure Mystery

Does this matter what time of day?

Are you on a well?

jeffcubsfan
Re: Water Pressure Mystery

Thanks. I'm not on a well. My neighbors haven't experienced anything similar. Also, the time of day doesn't seem to affect the issue.

Condoman
Re: Water Pressure Mystery

It could be the pressure balancing part of the shower valve. I don't think that is part of the cartridge. You could look at a parts diagram for that unit and see if it could be the problem.

HoustonRemodeler
Re: Water Pressure Mystery

Take the escutcheon plate from the valve assembly and snap a picture. A model number would be handy

jeffcubsfan
Re: Water Pressure Mystery

Thanks, all. Last night, I checked on my hose fixtures to ensure that they hadn't frozen and punctured. While that wasn't the case, I noticed that the problem exists on these too. It seems as though the problem is easily seen on faucets that don't have aerators. Therefore, I think there is an issue with the main feed line. Thoughts?

dj1
Re: Water Pressure Mystery

Do you have a pressure reducing valve as your main water line enters the house?

Fencepost
Re: Water Pressure Mystery

Is there an expansion tank above your water heater? (There should be.) If so, this could be the explanation. There are a few possibilities that I can envision:

  • As water is heated, the expanding water backs up into the expansion tank. This results in an increase in pressure in the pipes (the water meter prevents the pressure from backflowing into the city main). When you open the faucet, you notice higher flow rate until the expansion tank is emptied.
  • When water is not flowing, the city water main builds up pressure in your pipes until it reaches what is known as the "static pressure." When you open the faucet, this static pressure is held until the expansion tank empties. A restriction in the incoming line (such as at the water meter, a pressure reducer, or corroded pipes & fittings) causes a reduction in water pressure.
  • You have a pressure regulator that is faulty and allows pressure to build up when water isn't flowing but is unable to maintain that pressure when water IS flowing.
jeffcubsfan
Re: Water Pressure Mystery

Thanks, Fencepost. I do have the expansion tank above my water heater. Since I seem to experience the problem at hose faucets and in the shower with only cold water, I believe I might have a clogged supply line. Any thoughts on a good way to clear it?

Mastercarpentry
Re: Water Pressure Mystery

The WH expansion tank should be on the cold (inlet) side, thus if it is assisting pressure temporarily it will exhibit the same effect on all cold water lines because that's what it is acting upon. It's put there because with the hot faucets closed, any expansion can only go the other way- back into the cold water inlet.

It sounds like a pressure regulator issue to me. Look for a water pressure regulator by tracing a cold line back to where the cold water comes into the house- you may find it anywhere between that point and where the first pipe or fixture draws from, although they're usually located wherever the water line enters or very close to it. Also check at the meter box; a retrofitted regulator may have been located just downstream of the meter in more temperate climes where it won't freeze. Not common but I've seen it happen here a bit.

Phil

jeffcubsfan
Re: Water Pressure Mystery

Phil, You were right. I had a plumber out to diagnose the issue. He blamed the pressure regulator valve. The amount he wanted to charge for replacing this was ridiculous. Is this something an amateur can handle on his own?

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