Hot water boiler pressure high

My Dunham/Bushe residential boiler is a hot water boiler with a forced hot air central heating system. It has been running at a high pressure (30 lbs.) and this is causing the pressure relief valve to release water. I drained the expansion tank (which was full) by shutting the feed and opening the drain valve. It is an old system with no compressed air in the tank, which I believe does not have a bladder in the tank. It does have a shut off valve below the inlet to the tank and a drain valve with a hosecock connection on the opposite side. The inlet and drain are both on the bottom of the tank. After I drain it the system functions fine for a day until the pressure builds up and the tank is full again. I think I am bleeding it right, or am I? The pressure relief valve does go off due to the high pressure, but does seem to seat well after the pressure goes down. After reading some of the postings on the board, I also thought that the temperature setting on the aquastat may be too high. It is currently set at 160 as the high and 130 as the low with a 10 degree differential. What would the correct temperature setting be?
I would appreciate any assistance. Thank you, MRnice
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MRnice wrote:

I think you have a good understanding of the system and how that ancient exp tank works. Should work with those temp settings OK.
It's possible that an automatic fill valve from the incoming water supply is leaking and refilling the system, causing the high pressure. Find a shutoff valve and close it to find out.
Jim
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I am emptying the tank again to make sure it is totally empty. I think air will enter through the drain valve into the tank, which should be a good thing if I understand how this tank works. I will look for a valve on the autofeeder, I know on a steam system it regularly fills which you can see in a guage glass. I am not as familure with Hot water systems. I guess too much water would push up against the pressure relief valve causing the 30+ lb. reading on the guage too. Of course, I know this is a more difficult fix. If I wanted to run the boiler without the feedwater regulator for a while, how often would I add water to the boiler? How would I know when it needs it? Thank you for your suggestion, it seems like the only other reason for high pressure. The stack is clean, relief valve seems to work only at preset 30lb. and the temp. is not too high. Do these boilers require any cleaning , chamber, etc.? I have changed the oil filter, replaced a bad ignitor last season (my first season in home), and cleaned the flame scanner eye as well as changed the nozzle. Could lack of prior maintenance have caused sediment buildup to produce a high stack pressure causing a problem? Thank you for your advice, Ron
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MRnice wrote:

Unless there is a leak, that boiler shouldn't need feed water except in rare cases.
Oil-fired does need annual maintenance for cleaning and combustion air setting, etc. But that's not part of this problem.
That has to be a cast iron boiler, so there are no tubes. Get the pressure under control and see if there is any evidence of leaks. Jim
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I also wonder if one of the tubes could be leaking inside the boiler. There is alot of water on the floor, but I thought it must be from the Pressure relief valve blowing down.
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if the expansion tank is filling with water when the system is in operation , then the tank has an air leak and air is leaking out, letting water in... then when the tank is full of water, the pressure will build excessivly when the water is heated..
the air leak may be very small, like a tire with a small leak...
Mark
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Each time I emptied the expansion tank, I opened the inlet valve and it seemed to fill. I closed the automatic feedwater regulator and the tank did not fill when I opened the inlet valve this time. I emptied the remaining water in the tank and put boiler on. My well water pump had a problem right before this happened and the water to the house was cut off for a while. Maybe some sediment ended up in the autofeed reg. when water was restored causing it to stay on. I think you hit it on the head with the feed water problem. Is there any way of cleaning the regulator to possibly repair it before going out and buying a new one? Thanks, Ron
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Auto feeds go bad and can be innacurate new. Turn it off and the supply, filling a boiler for my house is a once year deal, I have 3 stories and keep 12-15lb cold. some systems need a bit more. Your pressure relief leaking is warning your pressure is to high, eventualy a boiler leak can develop. Im just a homemoaner here, no pro but I would call the manufacturer of the boiler and find out operating pressure guidelines, less is better for boiler life. I would wait till cool and drain water till its 15lb, keep the water fill off and see what happens. If you have 1-2 story house 15 may be not needed as I say I run 12-15 on a 3 story with boiler in basement, 4 levels, old and new boiler run the same. If no heat gets to upper radiators add a lb when Cold and bleed running. A too small an expansion tank can cause the same symptoms, increasing pressure when hot. Filling a boiler constantly is not good for a boiler as scale develops , reducing efficiency and life, if it knockc its got scale.
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Thanks to you all for your advice. Everything seems to be fine so far with the feedwater valve closed. I guess I will just keep an eye on things.
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If it is the same as my Watts fill valve and safety, it is a piece of crap and you toss it away. If it was sediment under the valve seal, it would probably be flushed out by now. My heater has had four Watts fill valves in 25 years.
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