Welcome! Here are the website rules, as well as some tips for using this forum.
Need to contact us? Visit https://heatinghelp.com/contact-us/.
Click here to Find a Contractor in your area.

Boiler Pressure Issue Has Plumber Scratching His Head

Gamma Member Posts: 3
edited February 2015 in Gas Heating
Hello all,

I'll start at the beginning and try to be as thorough as possible (but I'm not super handy, so bear with me!).

I have a 13-year-old Peerless boiler (series MI/MH) along with a Peerless Indirect-Fired Water Heater (60 gal). Both have been working fine since installation (house has 4 zones, plus the water heater). 3 zones are baseboard, 1 zone is cast iron radiators.

Last week I heard a ton of swishing in the pipes when the heat kicked on (this happened in a couple of zones). I checked the boiler and the pressure was at 0. And I noticed some residual water stains on the PRV pipe (but they could've been old). Plumber came, we bled the zones and he replaced the fill valve and expansion tank (which was filled with water). Next day, the pressure rose to about 25 and I saw some dripping from the PRV (just a few drips an hour). When the pressure got to 29, I let some water out of the system and called the plumber back.

He wondered if the Extrol expansion tank he put on the day before was bad, too. Sure enough he took it off and the tank started spraying water (which he said he never saw before). So he replaced it again with another brand-new Extrol.
When he left, the pressure was about 18.

Two days later, the PRV is still slowly leaking and the pressure keeps creeping up. It was at 27-28 again today and rising so I let a little water out of the system. During this time, I've been keeping the thermostats in all the zones really low (60), because the boiler pressure seems to rise when the boiler is working.

The plumber seems dumbfounded. I've seen some posts where the culprit could be the Indirect Water Heater. Do my symptoms sound like it could be the water heater? I'm just confused as to why the pressure was at 0 to begin with. And now, why is the pressure constantly building?

Thanks so much for any help you can provide.



  • Paul48
    Paul48 Member Posts: 4,469
    Note the boiler pressure. Close the cold water feed to the indirect, and open a hot faucet, until the pressure drops to zero, or close. Does the pressure go down in the boiler?
  • Snowmelt
    Snowmelt Member Posts: 1,334
    Paul nice catch, shut off the domestic water,
    Shut off the cold going into the domestic water of the indirect water heater. That's one way of testing to see if you have a leak going into your boiler from the domestic side of the indirect water heater.
  • billtwocase
    billtwocase Member Posts: 2,385
    Although an indirect can feed into the boiler heat side, the pressure was zero before the feed valve and extrol was replaced. It wouldn't have been zero if the indirect was feeding in. Pics would help here. Where is the extrol located? Does it attach to the bottom of a Spirovent? Is it isolated by zone valves and flowchecks? I would test the air in the new tank, feed in about 12 LBS, then leave the feed valve off.
  • Gordy
    Gordy Member Posts: 9,514
    edited February 2015
    He did install the right size expansion tank? New tank was checked for air pressure equal to system pressure ISOLATED from the system? If there is an isolation valve to the tank did it get turned back on? Was the new PRV set correctly? Is the fill valve usually off, or on?
  • Gamma
    Gamma Member Posts: 3
    Hey guys,

    Thanks so much for all your responses. When I contacted the plumber again regarding a possible indirect water heater leak, he basically said the same thing as billtwocase above: if there was an indirect leak, the pressure would never have gone down to zero. Also, the pressure only seems to rise when the boiler is working, so he thought that was another strike against the indirect water leak. He told me to shut off the valves to the fill valve to make sure the new fill valve isn't letting in a little water. I'm doing that now. He did not test the pressure in the new expansion tank. And as far as size, it's the same size as the original tank which had the system working fine for 13 years. Plumber said he may have to add a second expansion tank.
    I'm not familiar with a Spirovent. But I will take a photo and attach once I see if my fill valve experiment yields any interesting results. Again, thanks for all your thoughtful responses.
  • icesailor
    icesailor Member Posts: 7,265
    That system (because it has an indirect) is most likely a cold start system. Especially if the system uses cast iron radiators, there is way too much water in the system for a #30 Extrol tank. It needs a minimum of a #60 for a cold start boiler/system.

    Amtrol used to give away a wheel calculator that no one used. But a system like that doesn't have enough expansion room with a small Extrol.

    If the fill valve (which was replaced) was bad, it wouldn't have added water. With the new fill valve, it maintains 10-15# and there's less room for expansion.

    You shouldn't ever get water out of the Schrader valve on a new tank. If you do, it must be a defective tank. You can actually take a #60 tank, adapt it to 3/4" hose, and connect the tank with a washing machine hose to any boiler drain in the system (bottom drain is a good choice) and connect it temporarily. If the problem goes away, the tank was too small. Personally, I'd put both the old one and the new #60 in. You never have too much expansion room. As far as all that Pumping Away and PONC hooey, the system doesn't care where the expansion goes, as long as it has a place to go. Or the relief valve pops opens at 30#. On a temporary basis, I've put them about every place you can. And the world didn't stop or end.
  • hot_rod
    hot_rod Member Posts: 16,332
    The cardboard "wheel" has been upgraded to electronic technology :) follow this link to a free sizer tool.
    Bob "hot rod" Rohr
    trainer for Caleffi NA
    Living the hydronic dream
  • SWEI
    SWEI Member Posts: 7,356
    Yes, but... They don't have parametric sizing for the smaller tanks.
  • icesailor
    icesailor Member Posts: 7,265
    edited February 2015
    Its like that First, RTFM.

    But some people don't like those people that read manuals. They know too much. The ones that don't, know more.

    Reading a manual is a sign of weakness and is to be avoided at all costs.
  • Lance
    Lance Member Posts: 209
    For what it is worth. An indirect fired water heater is year round. the boiler should be maintaining a minimum temperature. Since the old expansion tank worked, its size should be OK. Replacing expansion tanks requires matching the type and the pressure of the bladder without pressure from the system. this is best done before installing. If boiler is 12 psi set it between 12-14. If the bladder leaks it will be detected. Installed in a system, even if isolated by a valve, the bladder could leak during pressure adjustment yet show the proper pressure and it would not be discovered. Water from the Schrader valve when opened indicates a bad bladder, or someone filled it with water(unlikely).
    Assuming the x tank is good, there are only two sources to artificially raise the boiler pressure, a leaky prv and a breech between the indirect coil and domestic water pressure above the boiler pressure. A leaky PRV can be eliminated by shutting it off. Make sure the shutoff valve actually shuts it off and watch over a few days if pressure rises more than a few pounds. If tank is undersized pressure could rise 10 pounds or more. Usually a breech in the indirect coil will show a pressure rise quickly, but it depends on the leak rate and size and house pressure. SInce house pressure is usually above 30 psi the relief will discharge.
    Previous leaking and old relief valves can leak at lower pressures. When in doubt change it out.
    Also it is prudent to isolate the potable water from the boiler water system components for visual leak testing to make sure no cross contamination can occur. A pipe opening between the boiler and the indirect coil can achieve this. good luck.
  • Ironman
    Ironman Member Posts: 6,877
    A # 30 Extrol is definitely too small, if that's what you've got with a converted gravity system or with CI rads.

    Another twist on this scenario might be that not only is the expansion tank too small, but the system may have previously had some air trapped at the top of the rads which was acting as an expansion chamber along with an under-sized tank. When the new tank was installed, if the rads were thoroughly bled, then you lost that extra air cushion and with an under-sized tank, there was not enough room for expansion.

    Try Ice's recommendation and see if the problem doesn't go away. Leave the fill shut off once the system is up to 12-15 psi COLD fill pressure.
    Bob Boan
    You can choose to do what you want, but you cannot choose the consequences.
  • icesailor
    icesailor Member Posts: 7,265
    "" Assuming the x tank is good, there are only two sources to artificially raise the boiler pressure, a leaky prv and a breech between the indirect coil and domestic water pressure above the boiler pressure. ""

    Not so. The third way is thermal expansion. And if the tank is too small, especially when it is a cold start, it expands to 30#, shuts off, contracts, drops to below 12#, and adds a slight amount of water. Then, on the next heat cycle, the pressure rises to over 30#, and the PRV drips, eliminating the extra water. The burner stops, the water contracts to below 12# as it cools, the fill valve adds the lost water, and the cycle repeats itself until someone replaces the 30# PRV. This goes on until the boiler fails from all the fresh water introduced to the closed system.

    The solution to that is a larger tank or a larger expansion control device.
  • Gamma
    Gamma Member Posts: 3
    Again. Thanks so much for all your advice. I wish I could reply to each of you, but I'm overwhelmed and under-knowledged! Most of this over my clearance level. I did go to the Amtrol link for sizing. I have a combination of baseboard and radiators (baseboard sizing: 30, radiators sizing: 90 -- so I guess a 60 would make sense). Since shutting the fill valve (it's been about 18 hours), there may be a slight improvement in the pressure. It's only gotten up to about 22psi so far. There's still dripping from the PRV, but that might just need to be replaced at this point. I plan on leaving the fill valve closed a little longer to see if the pressure holds. I've attached a couple of shots of the setup.

    Thanks again!
  • Snowmelt
    Snowmelt Member Posts: 1,334
    Nice set up but I will pick on it, what size copper is used here. It looks like one inch, doesn't look like your going to get the full amount of btu out of the boiler. The secound thing is that air scoop, there has to be 18 inches before going into the air scoop. I'm almost guaranteed that you have air problem. You may want to add a taco 4900 air seperator.
    Let's have a picture of the indirect water heater.