water heater goes over pressure

[Maylar]

I moved into a 65 yr old house last May. Heat is oil fired baseboard, one zone, with a separate indirect hot water tank/heater. Both are by Burnham, and about 25 yrs old according to the inspector.

Since the first of this year I've been getting water blowoff through the pressure relief (T&P) valve. I had my oil company's repair guy come and he replaced the valve. It's still leaking, and in fact getting worse. Every time the water heater circulator runs the pressure exceeds the valve's limit and it spews hot water.

I put a 100 psi pressure gauge on a hot water faucet and it pegs past 100 when the circulator runs, within a minute or so. Interestingly, the cold water side does not increase pressure, it stays at 60 (regulated after my water meter).

There is an expansion tank on the boiler but not on the hot water.

So.. what's going on with this? Why does the hot water pressure rise but the cold doesn't? And what are my options?

Thanks for any insight.

Dave

 

[Geofd]

have you thought about putting a pressure reducing valve on your
water main????

 

[voletl]

There's no need for pressure reducing valve on the water main if it's just the hot water
what do you mean by your water heater circulator? Do you have a recirculating line?

 

[Maylar]

The water heater has its own circulator pump.

 

[voletl]

That circulator Is for the boiler zone that heaters the water heater. If youre saying that everytime that circulater turns on the relief blows your coil in the water heater could be broken putting boiler water into your waterheater.

 

[Maylar]

Yes, that's what I'm saying. But wouldn't the hot water be dirty if the boiler water was contaminating it?

 

[havasu]

What is your incoming water pressure to the house?

 

[voletl]

If there is a leak new water is being introduced to the boiler could make the water appear clean.

 

[Maylar]

What is your incoming water pressure to the house?

My town has high water pressure. I've had garden hoses burst on more than one occasion. There is a regulator in the main feed after the meter, and it was set for 80 psi. I dialed it down to 60 and the problem remains.

Is there any test I can do to verify or dispel the idea that there's a leak between the boiler and the domestic water?

 

[voletl]

It MAY not be a coil leak. I was thinking and if you did have a cracked coil the water pressure entering the water heater would be greater then boiler pressure causing water heater water to enter the boiler blowing the BOILERS relief vavle as well

 

[Maylar]

So, I'm considering putting an expansion tank on the system to absorb the increased pressure. At least as an experiment, to see if the problem goes away. I can connect a tank temporarily via any one of the faucet valves and if it fixes the problem, plumb it in permanently.

Question: what size tank would you guys recommend for a 40-50 gallon water heater? And does it matter if it's installed in the cold or hot side (I've seen debates on both sides)?