Prestige Solo 110 Pressure & Condensation

You have about 25 gallons in the radiation, also have water in the plumbing and in the boiler itself, so you're probably getting close to 30 gallons of total system water, which means the EX15 is marginal unless you keep the system temp under 150F. The EX 30 is definitely the better choice. If you fill and pressurize the system to 12psi with cold water you'll likely hitting 30 psi and releasing water at the PRV if the system ever reaches 180F.

To make any sense of comparative temperature readings of metals with an IR instrument you need to put a dab of highly emissive paint or wrap of tape of high emissivity (the black tape used for hockey sticks is good) on the surface, and measure the high-E material, not the bare metal.

It's possible that the leak point is pressure sensitive, and only occurs during the higher temp operation when the pressure is highest, but find it you must! A steady diet of fresh water in a heating system causes excess corrosion on the metals in the system (iron pump impellers can't really take it.)

If the direction of the pump flow is away from the system pressure meter ( and toward the higher impedance of the radiation or boiler), that would cause the measurement to drop when the system first fires up. If the pressure drops too low on a low mass boiler you will often hear the sizzle & bang of larger bubbles of water vapor collapsing at the heat exchanger (sometimes called "kettling"). This is really bad for efficiency, since the foamy water and water vapor in contact with the heat exchanger are less thermally conductive than micro-boil water, so less heat gets transferred, and more heat goes up the flue. On low mass boilers it's best practice to pump TOWARD the boiler, (and away from the expansion tank) so that the pump pressurizes it slightly above the average system pressure. If it's pumping away from the you may need to raise the pressure to 15-18psi to reliably avoid the sizzle, which would then give you even less margin on the EX15 expansion tank.

Here is a picture of my system and the water flow is away from the expansion tank.


As stated earlier, my system maxes out at 184F which is considerably higher than Dana's suggestion of 150. When my temperature is 184 and the pressure is 30, there is overflow coming out the pressure relief valve. Not much comes out, but could that be my reputed leak? As I said, the sound of water coming in to raise the pressure sounds minimal. I did notice the "kettling" this morning, but it does go away without adding water.

For $35 I think I'm going for a new EX30 expansion tank. If nothing else that will remove it from the equation.

Thanks all. I'll let you know.

Since water is essentially non-compressible, it doesn't take much volume change to change the system pressure...really, it is minimal. A properly sized expansion tank is crucial, though, to ensure you can compress air verses trying to compress the water itself - the pipes will only expand so much when pressure is applied (I think I remember copper piping burst point is over 3,000psi).

The kettling stops after a few minutes due to the rise in pressure as the system heats up.

I don't see any pumps in the picture. If plumbed primary/secondary the pump could be pumping toward the boiler (good, since is raises the pressure at the boiler), but if it's plumbed with a single pump for both the boiler & radiation it would mean it's pumping away from the boiler, lowering the pressure at the boiler, which aggravates the sizzle & pop. (Slow flow can also make it worse. What's the difference in the output temp vs entering temp at the boiler- as measured either by the boiler or by your IR thermometer on a piece of black tape on the pipes?)

If it's a single pump configured such that it's pumping away from the boilre & toward the radiation, when the Extrol 30 shows up- pre-charge the tank to 15psi and bump the cold pressure of the system to match.

As a sanity check on the operating limits by system volume and temp, see the table in the lower right on page 4. The boiler has about 2.5 gallons in it, plus a gallon or three in other plumbing, so with 25 gallons in just the radiators, figure 30-ish gallons for the system as a whole. Looking at that table reason it's spittin' a bit at 184F, and yes, that could very well be the "leak". As a test, pressurize the cold system to 12psi, program the boiler to a high-limit of 150F, see what happens. Even if the system volume is as high as 35 gallons it shouldn't pop the PRV at 150F.

Looking at your radiation table the output at 140F/60C average system temp should be enough to heat the place. A delta-T of 60C in a 20C room means the specified output is at ~200-210F. With panel radiators in a 68F room the output at 140F will be about 45% of it's 210F output.



You have:

T800 puts out 801 BTU/section-hr @ 210F, x 10 sections is 8,010 BTU/hr, x 0.45 is 3,600 BTU/hr

T700 puts out 774 BTU/section-hr @ 210F, x 41 sections is 31,734 BTU/hr, x 0.45 is 14,280 BTU/hr`

T600 puts out 679 BTU/section-hr @ 210F, x 9 sections is 6,111 BTU/hr, 0.45 = 5,500 BTU/hr

T350 puts out 436 BTU/section-hr @ 210F, x 62 sections is 27,032 BTU/hr, x 0.45 = 12,164 BTU/hr

Totaling 35,544 BTU/hr.

That would be a reasonable whole-house load number for a 2200' code min house at 0F outdoor temps. At bay area style mid-30s outside design temps you would still have about 2x the amount of radiation necessary to keep up at 140F average system temp. The min-fire output of the Solo-110 is about 28,000BTU/hr, so you still want to run at a temp where the radiator output is a large fraction of that or it will short cycle cutting into efficiency and boiler life.

But with ~30 gallons of water as thermal mass in the system you should be able to set it up to run at a fixed temp 125F output without short-cycling the boiler, which would guarantee that it's always condensing (90%+ efficiency), whereas at 184F output it definitely isn't condensing.

Rather than swapping out the expansion tank, try programming the boiler for a fixed output temp of 125F, set the thermostat to whatever temp you like and leave it there, (or limit overnight setbacks to only 5F or so below your normal temp, to keep the recovery ramp times reasonably short), and time the burns by observing the boiler on an extended call for heat (bump the thermostat up a few degrees if it's not calling for heat otherwise). If it's always more than 3 minutes to a burn (probably will be with your water volumes) you could even run it cooler and it would likely still keep up, and the cooler you can run the system, the more condensing efficiency you get out of it, and the smaller the pressure swings.

Depending on how tight and well insulated your house is you might even be able to heat with 110F out of the boiler, but recovery from setback would be slow, and you'd be heading toward short-cycling. This is where going with the Solo-60 would have been of use, since you wouldn't have to sweat the short-cycling issues, and you could get long nearly continuous burns during the coldest weather. The -110 is going to cycle at low temps, but as long as it's a handful of minutes per burn and at most a handful of burns per hour you won't be trashing the boiler.

Dana, the pump is inside the unit so you can’t see it. It sits between the Heat Exchanger and the expansion tank, so that’s why I assumed the water flow was away from the system. Also, that pipe is hotter quicker than the other one.

I measured the temperature with tape on the pipes and that made them more accurate. Thanks.

I replaced the EX15 expansion tank with the EX30 and that really doesn't appear to change anything. The new tank was pre-pressurized to 12#. The auto-fill valve is still set to 12#. The fresh water valve is on. When the unit is off and the internal temperature is in the mid 70’s, the pressure is usually between 23 and 28. When the unit starts, the pressure drops about 10#, but then works up to over 25, which reputedly is not good.

I cleaned the Antrol auto-fill valve and set the fill pressure to 12#. When I did this I shut all the valves (fresh water, radiator pipes to and from the heater) and released the overflow valve to get the pressure to 0#. After the auto-fill valve was back together, I opened the valve on the pipe from the radiators to the heater and the pressure jumped to 25#. That surprised me and I don’t understand how it could or why it increases the pressure. When I opened the valve on the pipe to the radiators from the heater, the pressure dropped to 20#. When I opened the fresh water valve some water flowed (enough to replace what the overflow valve released), but did not impact the pressure.

I’ve attempted to lower the max temperature on the unit from 184, but that doesn't seem to hold. We normally have the heater on only in the morning and evening. It’s off during the night and most days; however, lately it’s had to raise the inside temperature over 10 degrees which means it runs for over an hour or more.

I’m about ready to cry ‘UNCLE’ and call for service unless someone can explain:
1. Why does the pressure rise when I open the pipe valve that flows from the radiators?
2. Why is the boiler temperature so much higher than the pipes? The boiler temp is a digital readout and the pipes are measured with an IR pyrometer toward tape on the pipes. It takes several hours with the boiler off to get the temps to 20 degree differences.
3. Why does the pressure continue to hover around 25# even after the boiler has been off for 12 hours and the boiler temp is 80? This causes the pressure relief valve to ‘weep’.

Final update – I hope!!

I called for help. The guy that came out was great. He knew I was trying to fix it myself so he just told me what I needed to do. Also when he walked in the house and saw one of the radiators he gasped. He was the distributor of the Faral radiators and had sold them to me 20 years ago.

I digress – the issue was the auto-fill valve leaking, diagnosed because pressure pops when return valve (to boiler) is opened. If pressure popped when outflow valve opened it would be the expansion tank. He agreed that the expansion and auto-fill valve are usually on the return side, but Triangle Tube says both ways work. He turned the max temperature to 124 and turned off the Domestic Hot Water, although the boiler was not connected to DHW. I cleaned the auto-fill valve again and tested for a couple of days with the fresh water valve closed. The fresh water valve has been open for a couple of days and everything is great – pressure doesn't get over 20# and the house heats great.

Thanks everyone and have a great New Year!