Home>Discussions>INSULATION & HVAC>Expansion tank quick-fill knob - open or closed?
11 posts / 0 new
Last post
Re: Expansion tank quick-fill knob - open or closed?

As I understand this unit, it is known as an Amtrol Fill-trol system and has an automatic fill valve which is actuated by the diaphragm pressure in the expansion tank, which is pre-set at 12 psi.

It is designed to allow more water into the the piping/boiler system when the pressure falls below the 12 psi.

If you have an on/off knob on the Fill-Trol, try turning it to close.

Place a bucket under the Pressure Relief valve & temporarily open the PRV valve to get the gauge pressure back to 12 psi.

If you have an on/off water shutoff valve that supplies the cold water from the house to the system, turn THAT off as well & watch the gauge to see if the psi stays between 12 psi and 20 psi (hot water expands 5% when heated, so there will be SOME increase in pressure as the system heats).

If the system continues to hover around 30 psi & the PRV continues to open & spill water, chances are the internal bladder of the expansion tank has sprung a leak.

There is a simple way to check the expansion tank, so post back if you have a continued problem.

Re: Expansion tank quick-fill knob - open or closed?

Thanks so much for the info. Sounds like something I can actually do, which is a relief. This morning before work I actually did a short test similar to what you suggest; I let the furnace run for about an hour after getting the psi back to 12. During that time, the psi rose to around 18 (or at least not 20). It seemed to climb fairly steadily throughout the hour. I had to leave for work, and decided to turn the thermostat to off. After about 5 minutes, the psi read 15 again. Does any of that seem out of order to you? I'll be sure to do a longer test this evening.

Re: Expansion tank quick-fill knob - open or closed?


Those psi parameters are normal.

As noted, boiler water always expands 5%, so cold boiler water should read ~12 psi; hot boiler water should read up to ~20 psi, then go back down to 12 psi again when it cools & loses volume.

Don't expect the gauge needle to point directly to 12 or 20; changing atmospheric conditions & how high the water is heated under various heat loads varies during the day & have an effect on what the gauge needle says.

The flexible neophrene bladder inside the expansion tank acts like a coiled spring to absorb the heated, expanded water during the heating cycle.

Keep a pail under the pressure relief valve for the time being.

Post back if you have a problem.

Google "Amtrol Fill-Trol system", or "Fill-Trol" (without the quotation marks) to get various sites for more info on how the Fill-trol works.

Re: Expansion tank quick-fill knob - open or closed?

Wow, thanks again. It's a relief to hear about the psi changes. I'll definitely write back if things get out of whack again. But since I'm here, would you mind taking a guess as to why the pressure went so high after getting a new flame sensor? Are they even related? The only things different I noticed after the replacement was that the pilot flame seemed more robust than the old flame, and the damper on the chimney was left on 'open' instead of 'automatic' (or similar terms) by the technician. Could either of those be the culprit? Could it just be that once a pilot light goes out one should bleed the radiators again?

Re: Expansion tank quick-fill knob - open or closed?


I haven't a clue!

Neither changing the flame sensor or the damper setting should have any effect on boiler water volume.

It's quite normal for a tech to check out different parts of the system, sometimes just for curiosity, or to make sure he/she remembers how they work.

The Fill-Trol is nowhere near as common as the Extrol expansion tank, which is extremely common on hydronic systems, & is always combined with a pressure reducing valve that maintains incoming water pressure at the standard 12 psi.

The tech may have simply twirled the knob on the Fill-Trol to see how it worked.

That's MY best guess.

There is no need to bleed the system of air now unless you hear air noises inside the pipes when the hot water is circulating.

Re: Expansion tank quick-fill knob - open or closed?

Unfortunately, my problem remains. 90 minutes of running the furnace led to a psi of 28 and a slowly leaking pressure release valve.

One clarification. The knob I was talking about is not the fill-trol; it's something called the quick-fill knob. The fill-trol is there; a gray knob that says 'do not adjust'. The quick-fill is another knob that says open and close. I wish i could attach a picture but can't figure out how.

So, how do i test the expansion tank?

Re: Expansion tank quick-fill knob - open or closed?


Before you check the expansion tank, could you advise if there is a shutoff valve between the house water supply and the boiler water supply; the "quick fill" knob you mention may be the valve I'm thinking of.

If you can find such a valve, shut it off to prevent any additional water from entering the boiler from the house supply.

A quick test of the ET is to remove the plastic cover from the little air valve at the bottom of the ET (if there IS a cover).

The air valve looks like a regular bicycle tire or auto tire valve.

take the edge of your thumbnail and quickly depress the little needle valve to let a little air out, and quickly let go.

Examine your thumbnail closely; if there is even a hint of water or moisture on your thumb/thumbnail the ET probably has a leak.

Also advise if there is a shutoff valve between the boiler piping and the ET; this valve, if it exists, will isolate the ET from the rest of the boiler piping.

If you get any water from your quick test you will have to shut off the water supply to the ET so you can unscrew it off its fitting.

If water is detected during the thumbnail test, the boiler has to be turned off, & the ET has to be removed for further testing.

Please advise.

Re: Expansion tank quick-fill knob - open or closed?

Again, you're a life saver.

I didn't feel any water, but air certainly escaped as you said. So I guess that's a good sign. What next?

Oh, and see pic 1 for a shot of the quick-fill knob, though i now think it is just a redundant safety valve to keep water out if the main water valve (just out of the frame to the left) isn't working.

Re: Expansion tank quick-fill knob - open or closed?


Good to see the photos, and that you've learned to post them.

But now I'm confused.

It seems you have an Extrol Model 15 expansion tank connected to a Fill-Trol Fill Valve.

You're supposed to have a Fill-Trol Model 109 tank on your system for it to operate properly.

It looks like the tank has been on there for some time---how long would you say???

The Fill-Trol fill valves have the reputation of being a real pain in the a**.

There's a little check valve inside that is pushed open by the force of the 12 psi charge in the tank, & is supposed to close when water pressure in the system gets to 12 psi.

However, any mineral deposits in the water can cause the valve to stick open, causing water to keep filling the system til it gets over 30 psi, thus tripping the pressure relief valve.

As noted before, if you can shut off the water supply by closing the "main water valve" you mentioned in your last post, you can keep the heat on til you can effect a repair.

If it turns out to be the fill valve, some heating supply houses sell them separately for ~$22.

What's the pressure gauge reading now???

Re: Expansion tank quick-fill knob - open or closed?

Ugh, it's never good to hear that a system wasn't installed properly.

The date stamp on the expansion tank suggests it's a little more than 6 years old (stamp says 11113701 - i'm guessing 11/01 as the date). At the least, it's been here since 2004 when we moved in.

I'm doing another furnace run this morning. I'll list psi and water temp over a 90 min period.

psi: 10
water temp: 70 (or lowest setting)

psi: 11
water temp: 110

water temp: 125

I'll update until 8am.


Temp: 140

Temp: 150

psi: 19
Temp: 155

Sponsored Stories

TV Listings

Find TV listings for This Old House and Ask This Old House in your area.