Low Pressure on Hot Water Circuit

[Lowmiler]

Over the last several months, we have noticed water pressure dropping while showering. Further investigation shows the pressure drop to be throughout the house and isolated to the hot water circuit.

Attaching a pressure gauge to the municipal water supply, after the inline pressure regulator, shows about 58psi, and drops to around 53psi when any kind of water use happens, hot or cold. This seems normal.

Same pressure gauge when attached to the hot water return line (we have a circulator), shows 58psi and drops to around 10psi when two or more hot water sources are used (shower and kitchen sink for example).

There is no easy way to tap into the cold water supply to the water heater or the outlet of the water heater. Test was done while circulator pump was running, so that was not a restriction.

The water heater is an indirect design, and is about 16 years old. It is a Weil-Mclain brand and should be stainless steel and good for 25-30 years.

Our water is just slightly hard, and there is no evidence of scaling or build up anywhere in the house (I even cracked open one of the flow check valves on the cold water supply and it was clean as a whistle).

I have noticed that there is a corrosion build up on the inlet and outlet unions of the water heater. I am not familiar with these types of unions, and thus not comfortable cracking them open to see how extensive the corrosion may be internally. Photo attached.

I am kind of at a loss where this restriction may be living on the hot water circuit and looking for suggestions.

Thanks,

Todd

 

[Reach4]

For another data point, put your pressure gauge onto the drain valve for the WH.

 

[Sponsor]

 

[Breplum]

there is a constriction in the supply

 

[Fitter30]

Mineral deposits driven out of the water at the highest temp. Higher the water temp the more minerals deposit. Dielectric unions are not a big deal. Plastic piece that u can see between the nut and brass. Flat gasket between flat mating joint. You tube it. Purchase a dia union because flat gasket will have to be change and possibly the plastic ring can be cut to wrap around the pipe. Inspection mirror and flashlite. Seen hot water lines total block.
Been short of hot water? Volume?

​

 

[Breplum]

A plumber might be your best bet to remove and replace the dielectric unions, or even convert to WH flex after a reducing coupling.

 

[Lowmiler]

For another data point, put your pressure gauge onto the drain valve for the WH.

Unfortunately, the WH does not seem to have a “hose bib” type drain, it relies on a siphon effect from the pressure relief valve to drain. Weil-Mclain Plus 100 model. So I’m not sure how to grab a reading there.

 

[Lowmiler]

A plumber might be your best bet to remove and replace the dielectric unions, or even convert to WH flex after a reducing coupling.

I think that’s my next step. I’m not ready to open that can of worms on my own. The external corrosion shows they obviously need some sort of service.

 

[Reach4]

Unfortunately, the WH does not seem to have a “hose bib” type drain, it relies on a siphon effect from the pressure relief valve to drain. Weil-Mclain Plus 100 model. So I’m not sure how to grab a reading there.

New to me, and a little shocking.

What kind of pipe comes off of the T&P relief valve or the drain valve? Copper, steel, what?

https://www.weil-mclain.com/sites/default/files/field-file/indirect-fired-water-heater-manual_1.pdf

 

[Lowmiler]

New to me, and a little shocking.

What kind of pipe comes off of the T&P relief valve? Copper, steel, what?

You can see the actual relief valve in the background of the photo I originally attached, the tubing that connects to its outlet is pvc. The house as a whole is built to a very high standard, according to my own observations, and those of multiple subject matter experts I’ve used over the last few years, so I don’t think this install was done wrongly. The operation manual from Weil-McLain for this model confirms it, too.

 

[Lowmiler]

From the manual.

 

[Reach4]

You can see the actual relief valve in the background of the photo I originally attached, the tubing that connects to its outlet is pvc.

It might be CPVC, which is rated for higher temperature. While that is usually in copper tubing size (CTS), it is also available in schedule 40. Nominal 3/4 inch CTS is 0.875 OD, and schedule 40 is 1.050 OD.

I am not a plumber. To take the pressure of inside of the tank, one thought was to put a Sharkbite TEMPORARILY onto the output of the relief valve, and adapt to a pressure gauge. I am sure that is in literal violation, and if you left that in place it could be catastrophic.

The objective of measuring the pressure in the tank, while you get your symptom, is to identify if the constriction is before the WH or not. Temporarily removing the vacuum breaker and attaching a gauge could be another way. I think most places don't require a vacuum breaker if the WH is on the bottom floor.

OK, here is a simple test to confirm your symptoms. Attach a GHT pressure gauge to the hot laundry supply. I understand that you feel confident the gauge will show low pressure during the shower, this is an easy enough test IMO.

One more thing comes to mind... make sure the supply valve to the WH is fully open. Somebody could have turned that-- a child or absent minded adult maybe. Also check to see if there is a valve on the output of the WH. That is rare, but the one on the input is almost always there.

 

[sajesak]

Over the last several months, we have noticed water pressure dropping while showering. Further investigation shows the pressure drop to be throughout the house and isolated to the hot water circuit.

Attaching a pressure gauge to the municipal water supply, after the inline pressure regulator, shows about 58psi, and drops to around 53psi when any kind of water use happens, hot or cold. This seems normal.

Same pressure gauge when attached to the hot water return line (we have a circulator), shows 58psi and drops to around 10psi when two or more hot water sources are used (shower and kitchen sink for example).

There is no easy way to tap into the cold water supply to the water heater or the outlet of the water heater. Test was done while circulator pump was running, so that was not a restriction.

The water heater is an indirect design, and is about 16 years old. It is a Weil-Mclain brand and should be stainless steel and good for 25-30 years.

Our water is just slightly hard, and there is no evidence of scaling or build up anywhere in the house (I even cracked open one of the flow check valves on the cold water supply and it was clean as a whistle).

I have noticed that there is a corrosion build up on the inlet and outlet unions of the water heater. I am not familiar with these types of unions, and thus not comfortable cracking them open to see how extensive the corrosion may be internally. Photo attached.

I am kind of at a loss where this restriction may be living on the hot water circuit and looking for suggestions.

Thanks,

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The rate of flow of the hot tap in the kitchen is 2l/minute, which checking online is ridiculously slow (this has always been the case - it's not reduced suddenly). Upstairs it's better, though I haven't measured it. I'm wondering if it's worth checking all the plumbing, working out why it's so slow, and seeing if it can be improved. Can anyone suggest what to look for, please? Or should I just accept it and live with it, which we have done for many years.

It doesn't help that it takes a good 2l runoff before it even gets hot. I catch the runoff in a large bottle and try to find uses for it, and have often finished the washing up before the water gets to a decent depth - but at least I can rinse each item under the tap as it's still filling.

 

[Lowmiler]

It might be CPVC, which is rated for higher temperature. While that is usually in copper tubing size (CTS), it is also available in schedule 40. Nominal 3/4 inch CTS is 0.875 OD, and schedule 40 is 1.050 OD.

I am not a plumber. To take the pressure of inside of the tank, one thought was to put a Sharkbite TEMPORARILY onto the output of the relief valve, and adapt to a pressure gauge. I am sure that is in literal violation, and if you left that in place it could be catastrophic.

The objective of measuring the pressure in the tank, while you get your symptom, is to identify if the constriction is before the WH or not. Temporarily removing the vacuum breaker and attaching a gauge could be another way. I think most places don't require a vacuum breaker if the WH is on the bottom floor.

OK, here is a simple test to confirm your symptoms. Attach a GHT pressure gauge to the hot laundry supply. I understand that you feel confident the gauge will show low pressure during the shower, this is an easy enough test IMO.

One more thing comes to mind... make sure the supply valve to the WH is fully open. Somebody could have turned that-- a child or absent minded adult maybe. Also check to see if there is a valve on the output of the WH. That is rare, but the one on the input is almost always there.

Supply valve to WH is fully open, no valves on main run after the WH within 20’.

Pressure gauge on the laundry hot water shows 58psi with nothing running.

Turning on hot water in kitchen drops to 45psi.

With that running and turning on shower, it drops to 35psi.

 

[Reach4]

A drop to 45 or 35 psi is enough to be noticed in a shower, but maybe into in a kitchen. But those pressures do not paint a clear picture to me. [edited]

 

[Lowmiler]

A drop to 45 or 35 psi is significant, but not enough to explain only 2 liters per minute at the kitchen hot. Confirm that cold at the kitchen gives at least 5 liters per minute.

That wasn‘t me who made that post in this thread about the 2 lpm, I’m not sure why that person felt the need to jump into this thread and confuse the issue.