Hot Water Heating System has high pressure

moallen

I have a Buderus G115/28 Oil Boiler (mfg 2005), 112,000 btu input with a Reillo 40 F3 Oil Burner, Honeywell L8124L 1011 Triple Aquastat Relay and a Taco SR503 3 Zone Switching Relay.

This heating season the pressure relief valve started dumping a couple gallons a day. When this happened the pressure was up around 35 lbs. I noticed the pressure would normally run between 15 and 30 lbs, depending on what was going on.

I replaced the Amitrol/Extrol Mod 30 Expansion Tank about a week ago. It had been installed in 2005 along with the Buderus boiler. It was water-logged and replacing it did fix the problem with the relief valve dumping hot water. Everything seems to be working fine.

But I've noticed ever since replacing the expansion tank, the pressure stays right on 30 lbs all the time. I know most would say that's way too high. The specs on the boiler show a 58 lb max pressure, but go on to show a 15 lb minimum and a 30 lb maximum with a 32 lb relief valve installed. The specs also show it with a 50 lb relief valve, but I have a 32 lb relief valve.

I've seen several posts about adding water when the pressure is too low but didn't see anything about lowering the pressure. I assume that would involve draining off some water. Or maybe I should just leave well enough alone? In any case, I thought I would see what people more knowledgeable than me think of this situation.

Jamie Hall

Do you have a feed through a pressure reducing valve from your domestic water? If you do, that valve may be the culprit. It should be set to add water at more like 12 to 15 psi.

moallen

Yes, it has a Taco 329-3 Pressure Reducing Valve. It has a fast fill lever that is in the A position for automatic operation.

From its instruction sheet, it sounds like I would turn the adjustment screw CCW to lower the pressure. But it doesn't look like anyone has ever moved the adjustment screw. Maybe it's failing (leaking) internally?

There is also a Watts 9D-M3 Backflow Preventer on the inlet side of the pressure reducing valve. I would think that is to prevent boiler water from backing up into the water supply lines and would cause low boiler pressure if it was failing.

If I change the pressure reducing valve adj screw, will I also need to bleed off some pressure or water?

Maybe I should also mention when I changed out the expansion tank the boiler pressure was at 20 lbs. So, I brought the new expansion tank up to 20 lbs before I installed it. Now the system no longer swings between 15-30 lbs but stays at 30 lbs.

Jamie Hall

You would know if the backflow preventer were leaking; they are designed to to show that. My guess is that the pressure reducing valve is leaking. There should be an independent shutoff on the feed to the boiler. Close that valve and drain just enough water from the boiler to bring the pressure to 20 psi -- no more draining than that, and it won't be that much water. Then watch it through an entire heating cycle. The pressure should rise slightly as the boiler heats, but then should drop right back to 20 when it all cools off again.

That would pinpoint a problem in the automatic feed. However, you shouldn't leave it with the feed shut off for any length of time. Get it repaired of replaced.

moallen

Ok - thanks! I just closed the feed and drained enough water to lower the pressure to 20 lbs. I'll keep an eye on it and report back.

moallen

Here's what I'm seeing after watching a couple burner cycles. At the high end: 25 lbs at 190 degrees and at the low end 10 lbs at about 122 degrees.

My aquastat is set for a low of 180, high of 200 and diff of 15. My main zone (3) thermostat is set at 67 degrees and it's 13 degrees outside here in south central NH.

I notice the circulator pump for that zone rattles when the pressure drops below 15 lbs. That can't be good.

I'm new to a hot water heating system but am trying to learn. Is a pressure swing of 10-25 lbs normal? Seems like too much to me.

lchmb

I would lower your temps...high of 180 low of 160. I would pull your expansion tank and make sure it is set to your cut in pressure of your fast fill or just a touch below it. Generally when I set a system to 13 lbs I see it increase in pressure to 20-22lbs when at temp (180) which is normal expansion of the water being heated

STEVEusaPA

Maybe you need a bigger expansion tank. My system pressure hardly moves, maybe 2-3 lbs between 120° water and 190° water.
I would make sure the system is fully bled of air. You don't say how high it is from the boiler to the highest radiation in your house, so I can only tell you if it's a 2 story house I would settle in on 15lbs at 190° water.
I would put on a LWCO, and close the feed valve.

moallen

Looks like Jamie was correct in suspecting my press reducing valve is leaking. With the feed shut off and after monitoring the pressure and temperature throughout the day, this Buderus "low temperature" boiler is operating at design specs.

So, there were two problems. The Amtrol expansion tank was definitely waterlogged, which I replaced. But the Taco pressure reducing valve is also bad. I'm going to order one tomorrow. For now I'm leaving the feed turned off.

In case anyone is interested, I set a laptop up by the boiler and connected a usb camera pointed at the boiler's temp/press gauge. The laptop is on my home network, so I can monitor the gauge upstairs without hanging around in the cold downstairs garage.