Boiler empties when heat turns on - up to 12 hours for condensate to return

Old 02-14-21, 01:34 PM
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Boiler empties when heat turns on - up to 12 hours for condensate to return

We have been encountering issues with our boiler/steam radiator system this year, with the boiler nearly entirely emptying when the heat turns on, and then taking 10, sometimes 12 hours recollect the condensate.
A typical day in the winter includes

Overnight - heat usually does not turn on, thermostat set to 63ish

8am - water is usually 2/3 in the sight, heat turns on, thermostat set to 67

9am - low water light turns on, water is 1/4 or often less in the sight

After this, heat will not turn on, hot water enough for sinks (sometimes), but not showers (tankless system).

It then takes until 6, 7 or 8pm for water levels in the sight to return to between 1/2 or 2/3 where we're confident enough to use a shower, etc.

Our radiators seem to be appropriately pitched, though they sometimes spit a little water. Some light knocking, but not anything like a hammer.

We had someone come out to look at it, and he was focused in on an issue with the boiler (we had a faulty low-water sensor we're glad he caught) that he didn't look beyond the boiler itself.

Any theories? We are in a 100 yr old home, which is why we're on steam, and my thought was settling could cause the pipes to be off-pitch? Any other thoughts?

Old 02-14-21, 04:33 PM
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To start with if possible pics would be helpful of your boiler and near boiler piping. Do you have 1 or 2 pipe steam.

Start at the boiler and make sure all your pipes are pitched back to the boiler. You should not have any water coming from your vents. They are there to let air out and then close when the steam hits to keep it in the rads. When the steam cools down it turns to condensate and returns to the boiler.

Any amount of banging, a little or a lot is the steam hitting the condensate which means the condensate is not draining back to the boiler. A system that old may have corroded wet return lines preventing water from returning to the boiler.

You can always add water but that is not a good idea because once the initial water returns the system will be overfilled.

If you have dirty or oily boiler water it may be getting syphoned up into your system instead of staying in the boiler and making steam. What does the water in your gauge glass look like. It should be clear.

Has there been any work done on the system lately or did you always have that problem.
Old 02-15-21, 05:10 PM
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I have to disagree with you spott. Steam pipes have to be pitched away from the boiler towards the returns. If they are pitched back towards the boiler the steam and condensate will fight each other and you will get banging not to mention that the steam will pick up moisture and cause spitting at the air vents. As far as the issue here, it sounds to me that there is a clogged wet return not allowing the condensate to get back to the boiler. The dirty or oily water in the boiler will surely cause the water to disappear from the sight glass and get carried into the system. And if the returns are clogged with mud it will carry back into the boiler and contaminate the boiler water.
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Old 02-22-21, 04:29 AM
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Depending upon the type of steam system this is, the steam piping can slope upwards or downwards. In both systems the steam and the condensate flow in the same pipe either in the same direction or counterflow.. If the condensate takes many hours to return to the boiler I would suspect that the boiler return piping needs attention. It could be restricted or plugged. The age of the house tells me that the problem is in the return piping. There are many types of piping systems that were used over the years so giving an exact fix for your problem is not possible unless we are "on site". It is time to have an expert steam guy look at your system.. my 2 cents.
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Old 02-22-21, 05:55 AM
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I lived in an old house for a year. The boiler was new but the hundred year old radiators were not. Most of them leaked. I had to add "make up" water every couple of weeks. The manual for that boiler (New Yorker) mentioned adding make up water as routine maintenance.

I would add fill water until it reaches 2/3 up the sight glass and see what happens.
Old 02-22-21, 02:02 PM
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With all due respect to cw, as was mentioned in post #2 that is really not a good idea because when the origional water finally returns you will have double the needed water which will end up in the pipes and possibly rads and then you will really have a problem. You will end up draining the excess water and with an overfilled boiler there will be no room to make steam.

As was mentioned in all posts it looks according to the limited info given your return line or lines may be obstructed preventing conensate or water to return to boiler.

Pics would be possibly helpful to see what you have.
Old 02-26-21, 05:54 AM
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Steam system piping can be parallel or counterflow types which means the condensate runs the same way as the steam or opposite direction. There are systems that the steam main goes uphill from the boiler so condensate drains back to the boiler and then converts to a parallel so the condensate runs downhill away from the boiler in the same steam main. Many systems incorporate both one pipe and two pipe system in the same piping. One and two pipe systems refer the the amount of pipes at the radiators.
Anytime the water level stays low for a period of time after the boiler is running tells me the returns are slow to return the condensate. The condensate return should not take very long to come back. The return must return fast enough to replenish the water level in the boiler to give continuous operation.
If the return pipes are exposed and the water disappears from the glass and your saying it takes hours to re-start the boiler are the return lines warm to the touch?
My experience is when the returns, also called the garbage dump of the system, are slow they are nearly blocked. The good news is after 10-15 ft from the boiler they are usually not to bad. I would cut the return out at 5" increments until I got a return pipe that was over 1/2 the diameter of the pipe open. Thread the black pipe and re-pipe back to the boiler in copper or iron. Copper is OK below the water level of the boiler. The other thing I did was pipe the new return pipe one size larger than what was there prior. All the work you are doing will loosen up some dirt in the remaining return pipe. If possible flush existing return before connecting new return line.

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