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No Hot Water Pressure

We just changed the mixing valve on our Smiths boiler as we didn't have any hot water. It fixed the hot water, but now our water pressure for the hot water is gone. It pulsates and when you turn on another faucet it almost stops. We have tried removing the air from the lines and nothing. Any ideas?

Re: No Hot Water Pressure

What type of system is it? If it's a coil then it may be plugged.


Re: No Hot Water Pressure

Also check how the mixing valve was installed---these valves are usually marked so you put the "cold" water connection in one side, the "hot" water connection in the other side, and the "Mix", which goes to the shower head.

Re: No Hot Water Pressure

Thanks for the info. It is a cast iron Smith's. The valve is correct, we have checked all airators. Sounds as though there is air in the line as it will sputter a little and the pressure will improve for a bit, but then slow down again. We just had it looked at in October and it was clean. When we were first trying to figure out why we didn't have hot water, someone told us to check the zone valve by lifting up the "L" lever. When we did that the t&p guage went to 200 and stayed there. I am wondering if some sediment is stuck in that valve. I have hot water so that is good.

Re: No Hot Water Pressure


I'm having trouble understanding your posts---you have to realize that the DOMESTIC HOT WATER that you use for showers, dishes, etc., is actually a separate system from the hot water that's used to HEAT THE HOUSE (boiler water).

The DOMESTIC hw is tapped from the cold water supply piping at the same high pressure & then (sometimes) goes thru a coil inside the boiler, as john mentioned, or a separate hw heater, or what's called a "sidearm"---it then goes to the HW taps for the stated uses.

The BOILER WATER is a closed system that circulates only thru the boiler & heating pipes & is held at a low pressure 12 psi (unlike the DOMESTIC which is usually high pressure 50-60 psi).

Boiler water (dirty, undrinkable) is never allowed to mix with the domestic hw.

Try to trace the domestic line from the point where it taps off the cold water supply to determine how it is heated (usually by a hidden coil at the front--inside the boiler).

There's usually an 8" round or retangular plate at the front of the boiler with a 1/2" copper pipe going in & one 1/2" copper pipe coming out for the domestic supply.

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