Pressure too high?

Old 01-10-10, 05:04 AM
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Pressure too high?

The plumber who came over to fix my boiler and bleed the system reiterated to me a few times that the pressure on the boiler should not exceed 20psi.

Well, what do you know .. it did tonight at 4am. Luckily I was awake and heard water dripping from the boiler -- so I went to check. Apparently, it had gotten to 30psi and water was coming out from the pipe connected to the reducing/relief feeder.
Turns out he had set the temperature to 190-200. Weird thing was that the system had been running all day on that temperature and it didn't happen till 4am.

So, I lowered it to 180 degrees and I see it now goes up to 24psi about. Is this still too high? I read a few threads where njtrooper said 180 at 24psi is fine. I've been watching the boiler turn on/off for the last hour and the maximum has been 24/25psi before it turns off.

Now, here's the other weird thing ... as I'm writing this message -- it turned on again and I went to watch it. It only went up to 21psi this time ... I did readjust the temperature to be exactly on 180 (whereas before it may have been slightly off at 179 or so).
Old 01-10-10, 05:49 AM
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Sounds like the air charge needs adjusted or the tank needs drained depending what type tank you have. The normal pressure for a hydronic system up to a two story home is 12 - 15 psi. The pressure should not change much from hot to cold.
He should come back and service the tank. If the tank is at the ceiling between floor joists it would require draining. If it is hanging from the piping the system pressure will need dropped to zero and the air pressure checked and maybe air added to the tank.
Old 01-10-10, 09:07 AM
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I read a few threads where njtrooper said 180 at 24psi is fine.
Be careful when taking things out of context! I don't know which threads you saw that in, but I probably said it was OK... not fine... and if I did say 'fine' it would have been in the context of that particular installation. I almost always will advise that if I see more than 5-8 PSI increase, I would want to check/adjust/service the expansion tank to be sure...

In SOME cases, 24 PSI could be fine...

You see, the maximum pressure in the system is entirely dependent on the ability of the expansion/compression tank to absorb the expansion of the water as it is heated.

At 180, the water has expanded a little under 4% in volume from room temp. From 180 up to 190/200, you will see perhaps another 1% expansion... and in your case that was enough to push your expansion/compression 'over the edge' and vent your relief valve.

I agree with rbeck that he should come back and service the tank... he should have checked that when he was there.

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