Furnace always building pressure

What is this device?

Please do not misinterpret my question as a testimonial to annual system drain and fill. All that does is introduce parasitic O2 that must be scavenged by chemical additives and/or driven off by heat.

No, I was simply attempting to assume why you should/ could, have an abundance of air in the system. You cold be flashing the boiler or a zone to steam if your not filed and purged correctly. Sounds like you had 24 hours of good running. Maybe you got it.

Worked well last season ????

The son went in for a shower while I was observing the guage and I noticed that the temp was at 180 and the pressure was at 17 psi. Soon after he put the water on the furnace started running and the pressure went up to 38 and the relief valve started spitting. So is the domestic water raising the pressure and not the boiler water? Last night it was pretty cold here in central PA and I am sure the boiler ran sometime through the night but it did not kick the prv. No domestic water was used through the night!

ODDSNENDS4U wrote:What is this device?

Page 12 of the BG link you have above.

Last season it worked great!! no problems at all. I am not sure if I am filling or purging the lines correctly? I refilled the system because the prv valve was leaking and did not want to take the chance of air in the system. But maybe I made matters worse!!

ODDSNENDS4U wrote:The son went in for a shower while I was observing the guage and I noticed that the temp was at 180 and the pressure was at 17 psi. Soon after he put the water on the furnace started running and the pressure went up to 38 and the relief valve started spitting. So is the domestic water raising the pressure and not the boiler water? Last night it was pretty cold here in central PA and I am sure the boiler ran sometime through the night but it did not kick the prv. No domestic water was used through the night!

Start at page 15 and read about expansion tanks. If fire raises the boiler pressure -- you don't have a working expansion tank.

I emailed honey well about the expansion tank. I sure hope they come with a warranty as it is only a little over one yeear old!! Den

Your email to Honeywell probably went into outer space.

The picture above is an air scoop with an air vent above it. Is the cap on the very top of the air vent loose to let air escape? Keep it loose. Depressing the valve stem will cause hot water to come out and sometimes they get clogged and don't seal up again, hence the cap. Maybe it isn't bleeding out the air like it should.

The sudden increase in pressure when the domestic hot water was used is a mystery. If you had a pin hole leak in the coil, the pressure would build whether or not the hot water was being used. I think we've pretty much ruled out the coil. Is it possible that house pressure is being introduced to the boiler through some sort of plumbing goof? Is there any other line from the house water connected to the boiler, except for the pressure reducing valve, that could allow direct/indirect house water pressure to get into the boiler? Perhaps a malfunctioning device?

stoker-man wrote:


Is it possible that house pressure is being introduced to the boiler through some sort of plumbing goof? Is there any other line from the house water connected to the boiler, except for the pressure reducing valve, that could allow direct/indirect house water pressure to get into the boiler? Perhaps a malfunctioning device?

Very simple system with no frills. What type of devise could be malfunctioning?
No goofy tieins!
Den

I've changed out many expansion tanks that were leaking by the bladder. It is possible to get an Xtrol tank and replace the Honeywell']. I have only seen leakers with no pressure. Any supply house will have an Xtrol model 30 or a 60 for a larger system.
Try to remember to buy the special valve that has a shutoff and a bleeder that goes between the air scoop and the expansion tank. That way you can remove the tank and replace because you now have a means to shut it off. The valve is about $8.00 and a new Xtrol tank is about $50. I think the big box stores have them if a supply house isn't close by.
I hope you are aware that you don't need to completely drain your boiler when you are doing a repair like this. Just enough to get it below the level of work, AFTER closing any open valves. If possible let it cool down somewhat, but it doesn't have to be stone cold and empty for a quickie exchange of tanks. The little Honeywell air vent in the top of your air scoop likely needs to be replaced. Only 8 dollars, and it sure would be easier while it is shut down.

The shower issue you mentioned sure indicated to me that the rubber ballast tank has been compromised. That can sure cause the pipes to bang also with no place to take up the expansion. I don't know about the warranty.
I hate to be the guy suggesting the 'parts swapping repair technique', but there just isn't that much to the system. It HAS to be one of the things we discussed.

PS: The ballast tanks used for water wells use the same type of expansion bladder(at greater pressure, obviously). They crap out regularly, usually notifying the user by banging or surging sounds. They will damage the pump controls (on-off, on-off all the time) cause short cycling, etc. and general 'water hammer'.

I forgot to mention. Never drain your hot water system for any reason other than repairs. Fill it and if it never needs added water for 50 years.......great. Fix any leaks immediately. Remember to check your coil gasket every year and snug up the nuts.

ODDSNENDS4U wrote:How do I power vent the system?

Power venting a system is a method to quickly remove all trapped air in the system. It requires valves to be in specific locations so that extra fill water at water main pressure can be introduced and simultaneously be drained or flushed out. I works by having sufficient water flow, flow much greater than your circulator pump can achieve, to move the trapped air along and out the system. Much like when you first connect a garden hose to a faucet. It gurgles until all the air is out of the hose. From what you describe it's unlikely you have valves in the idea location to "power flush".

One piping method for power flushing is as follows. Assume your circulator is on the supply side of the boiler and follows the air scope. Fill water via a pressure reducing regulator is normally introduced into the bottom of the air scope. If there is a bypass on this regulator to allow full force water fill AND a valve to shut off the boiler supply line prior to the air scope AND a drain port prior to this valve. Then by putting a drain hose on this drain port and applying full force water you will "power flush" the system when the supply valve is closed. Full force water will flow through the system in the usual direction exiting out the boiler supply line. It's important for the flow to be in the proper direction so any check valves can open. It's also useful to have valves on any zones so that you can direct flow through each zone independently. You will need to adapt this full flow idea to your particular piping situation, for example it would be slightly different if your circulator is on the return side of the boiler.

Power flushing is very effective. It can get the trapped air out of any system in a hurry.

stoker-man wrote:The sudden increase in pressure when the domestic hot water was used is a mystery.

Oh I know I am going to step on myself posting a rebuttal to the mfg rep

But why is this a mystery???

Grant a moment, my diagnosis of a faulty expansion tank. The appliance comes up in hi fire to satisfy the loss to the DHW coil but the expansion generated by that hi fire has no place to go because the zone pumps are quite.
so we have a - pressure change - because there is no place for the expansion taking place in the vessel.

Can you post some pictures of the whole set up? Something is being missed. Is there a DW feed piped in the bottom of the air scoop before the tank?

Here is a bunch of photos for you.
Thanks
Den