Log-Burning Boiler and "Closed System" Pressure Problem

SeanGMac · February 11

Hi all,

I wonder if someone can advise/teach me on this matter.

Firstly, I am in Finland where they like to do things differently.

We have a log-burning boiler which heats the water and radiators. It was installed in the 1990's and is situated in a cellar below the house. There are two lines of radiators in the house, one of 5 radiators and one of six. It is apparently a "closed system". There are two pumps in the overall system, one which pumps the water around the radiators and one which pumps the water around the boiler (I think). After heating the boiler I normally switch off this second pump as taught by the previous owner when we bought the house. Our water supply is from a well.

The presenting problem is that over course of 12 hours after switching of this second pump the pressure in the system declines to zero. The radiators by this time seem to be empty of both water and air. But if it is a closed system, where has the water gone? Our plumber thinks there must be a leak somewhere. I can find no evidence of this.

Is there an alternate answer to the missing water (and zero pressure)? I am clueless. If the water isn't actually leaking is it even a problem?

Intplm. · February 11

The circulators needing to be manually shut off once the system comes up to temperature? And no water in the system?

Im not sure how the radiators are functioning? How are they heating? What is the system pressure at start up? How are they getting water? After the system runs where has the water/pressure gone?

Would like to see some pictures posted here. A few of the system up close then a few feet away and the type of gauge.

SeanGMac · February 11

The radiators are full of water when up to temperature.

The pressure has usually fallen either to zero or very low by the time I light the fire next day.

There are gauges all over the place, some of which probably need recalibrating. The most relevant one however is new (new pressure tank just installed). I will take some photos.

Jamie Hall · February 11

A diagram of the system is going to help, if you have one or can create one. However, in the absence of one…

I presume that, in the morning when you go to fire up the boiler, you have to actually add water to the system to get water into the radiators? To belabour the obvious, if you have to do that, the water is going somewhere…

Now it doesn't have to be a leak. Are there valves connecting your well supply to this system? And is your well supply always pressurized? I can envision a scenario where the well supply comes in and one line goes to the domestic uses and the other to the boiler. If the domestic side has a check valve on it, it is possible that some combination of leaking valves on the heating side could let the water from the boiler back into the well. Not supposed to happen, but…

Otherwise, there pretty well has to be a leak somewhere. Can you close valves to separate the various radiators and their piping from the boiler? May have to wait for warmer weather. If you can, close them and see which of the two circuits loses water — then you'll have a better idea as to where to look.

And as I say, a diagram is going to help. I dare say that Finnish practice on these things is not quite the same as what we're used to…

Grallert · February 11

Is your boiler connected directly to your radiators or is there a large water storage tank acting as a battery? In this country we often see solid fuel boilers connected to insulated storage tanks that that are responsible for storing the hot water the boiler produces. This way the boiler runs short and hot and clean. I would love to see pictures.

SeanGMac · February 11

Water in from the wall on the right

SeanGMac · February 11

SeanGMac · February 11

SeanGMac · February 11

I have tried to post these as a journey from input to delivery-

Grallert · February 11

That big tan box looks like a storage battery with a coil there at the lower left where the boiler exchanges it's energy. Am I correct? That would lead me to believe the boiler side is a closed system. If the boiler is losing pressure and you can't see where I'd be concerned the submerged coil is leaking into that battery. But it looks like there is some type of make up water valve above the boiler, If so that should be adding water. Might be blocked up. If there is a leak in the coil and the make up water valve is working the storage tank will over flow eventually. But I bet the make up water valve, if that's what I'm seeing, is blocked up.

This is all assuming I am correct that the big tan thing is in fact a storage tank (battery).

Jamie Hall · February 11

I do see an expansion tank — is that on the boiler side of the piping? And, if so, is there water being lost from the boiler sidee, or the radiator side? If it's from the boiler side, I almost wonder if that expansion tank might be waterlogged and enough water getting forced out of the pressure reflief?

SeanGMac · February 11

Trying to answer some of the questions…

The water goes from boiler to tank - as see it. From there to radiators/hot water taps. Does that make sense?. The electric pump in the last photo is the central heating pump. That pump is on all the time so should be circulating the water all the time. In the mornings that pump is sometimes a bit noisy - I figure because there is a lack of water in the system?

I don't put new water into the system - heating the boiler alone raises the pressure up to function and fills the radiators. The pressure is meant to go up to 1.5 psi max after which the overflow is meant to engage. What I find is it that pressure can go up to 1.8 without that happening.

Between the boiler and the hot water tanks there is a valve which the former homeowner demonstrated should be engaged after heating the boiler and switching the pump off. It became stuck over time in the open position and is unusable now - someone, a previous plumber, perhaps, said it wasn't important and declined to fix it. Could this be important?

There is a gauge at the pipe from the well - since I lived here it hasn't worked (is at zero). I don't know if that is relevant or not.

SeanGMac · February 11

To Grallert,

My understanding is that the three coil-looking devices are inputs if we ever wanted to heat the water with electricity. Does that make any sense. As far as I know the water tanks are simply storage.

SeanGMac · February 11

Jamie,

Do you mean the red tank or the blue one behind it? Both are boiler-side, I believe.

The red tank is new - previously there were two smaller ones which had failed (i,e, were full of water)

Grallert · February 11

https://forum.heatinghelp.com/discussion/comment/1841969#Comment_1841969

Above that, the disc with two pipes, one at 12:00 and one at 3:00. Are those connected to the boiler in any way? And is that tank full of water? How do you know what the water level is? How would you add water to the tank?

Forgive my ignorance of your system. The way I see it: the wood fired boiler heats water and that hot water is sent to the tank. That tank hold a great amount of hot water to be circulated around in the radiators That tank should be full of warm if not hot water waiting to be used in the radiators. Is there a heat exchanger for the radiators? If not then the water level always need to stay above that pump (some how). There must be one for the domestic hot water. You only fire the wood side when the temp in the tank drops to a certain point? The place I would start is replacing all the faulty gauges so I could be certain of what is going on. Then move on to failed valves. I would think the is some device that maintains a safe water level and or pressure.

If the boiler and the tank are atmospheric There should be heat exchangers for the radiators and the domestic and there should be an expansion tank above the heating system with a sight glass for monitoring head pressure. Though that is what the new red tank could be doing? Sorry for the train of thought ramblings…

Jamie Hall · February 11

Ah! Major forward progress here. I assume your pressures are in Bars, by the way?

The entire system is basically one connected system as far as I can tell from your comments. Now what that implies is that that expansion tank — the red one — has one of three possible problems. It may simply be too small. If the system is really all connected, that's a lot of water. Second, it may not be charged with air correctly — either it never was (common enough) or it has lost its air charge (also common enough). There may be a port on the tank where you can measure the air pressure — I'm not familiar with that particular tank). The air pressure with the system cold should be right around 1 Bar. The third possibility is that it has failed… like the other two…

One way to handle things would be to replace that tank with a bigger one.

However, may I ask if there is an attic or loft space which is warm (at least above freezing) which is above all the radiators? If there is… a simple, large, vented tank or cistern up there, connected to the system (maybe with a float valve to ensure it maintains a level) which is connected to the system should take care of things…

SeanGMac · February 11

Jamie,

The loft is cold, unfortunately.

I believe the water storage tanks hold 1000 litres.

So that red tank was installed only 3 months ago. After fitting, I called the plumber back to adjust it as the pressure immediately fell to zero the next day. So he did adjust it and when I phoned him soon afterwards as it still kept falling to zero he told me to add more water to the system (until the cold pressure was 0.7). That seemed to work for a while, it was falling no lower than 0.4 but now we are back to square one.

I don't think the new tank has failed because it is not full of water like the two previous ones were.

So, from your reply, I need to get the plumber back to adjust it again (to which kind of limits?) or discuss with him the possibility of installing an even larger tank. Is that correct?. Fortunately we have not actually paid for the new tank because the plumber did not want to bill us until he was 100% satisfied everything was working as it should - he seems to be very competent and is certainly conscientious.

SeanGMac · February 11

Grallert,

Above that, the disc with two pipes, one at 12:00 and one at 3:00. Are those connected to the boiler in any way? And is that tank full of water? How do you know what the water level is? How would you add water to the tank?

From what I can see there is no direct link from the boiler to these discs. Those pipes are from one part of the tanks to another. The tanks hold 1000 litres, btw.

SeanGMac · February 11

What about this valve that is stuck - is it important? What I know about plumbing can be painted on the back of a postage stamp with a large paint-brush but it seems to me that the water is being delivered to the house vertically. As the pressure drops - and in the absence of a valve to stop it returning back - is it just falling back from the radiators and system when the pump is off?

Incidentally, there no gauges or other ways of measuring the volume of water in the tanks or in the central heating - only temperature and pressure gauges at various points.

SeanGMac · February 11

The valve that is stuck open:

Grallert · February 11

From what I can see there is no direct link from the boiler to these discs. Those pipes are from one part of the tanks to another.

It looks like that might be a mixed loop off of a heat exchanger likely for hot domestic water.

I can't imagine the the system was designed to drain back from your radiators every time that pump stops. It must make a terrible racket when it starts up. There must be something that was keeping the system full at all times, and that would be some sort of tank. Either a suspended cistern or the proper expansion tank. Neither will work however if there is no or not enough water in the system. Can you add water to the 1000 liter tank until the radiators are full (while the system is cool) and there is the correct pressure on the wood boiler?

SeanGMac · February 11

Neither will work however if there is no or not enough water in the system. Can you add water to the 1000 liter tank until the radiators are full (while the system is cool) and there is the correct pressure on the wood boiler?

I believe our plumber was thinking this when he told me to add water up to 0.7 (cold) before lighting the fire. There is only one place where I can add water to the system - the two black taps pictured above the boiler. Now, is the water I add from there filling only the closed central heating system or is it going into the tanks or both. I don't know - and there is no way of measuring how much water is in the tanks. I presume they are always full until such time as I switch off the pump.

Grallert · February 11

"Now, is the water I add from there filling only the closed central heating system or is it going into the tanks or both"

Good question. That is something you can tell I would think by keeping an eye on all your pressures and making sure you are allowing all the air out of the tank and boiler. If the tank and the boiler are closed/isolated from the radiators via an exchanger or coil that make this harder. I don't think that is the case though. I think that when you are filling you are filling against air, air in the radiators and air in the tank and perhaps air in the boiler.

Now I could be wrong, but I think you could fill to pressure go up stairs and vent your radiators, keep doing this until you get water from all your radiators while keeping an eye on anything that could over flow or over pressure and your leaking will be solve. It will either not reoccur or it will declare itself and it location.

In short I think air is your problem.

SeanGMac · February 12

Hi,

Thanks for your input, people.

So today I have added water to the system until it sounded like no more could be added - keeping an eye on the pressure gauges.

I then vented each radiator - they all seemed to be full of water only. A little air came from the first radiator in the shorter line but none from the remaining. I know that sometimes if you allow a good amount of water out there can be some air trapped inside which will suddenly emerge but it did not feel like this was going to happen.

After venting the pressure had fallen back to 1.2. I waited a couple of hours to see if it would fall any further which it did not. So I have now fired up the boiler. I won't be able to keep it going as long as I usually do at such a high starting point but that's ok. Tomorrow I will vent the radiators again before starting up and I figure if I do this over the next few days the pressure will bottom out to an acceptable starting point.

As far as the hot-water tanks are concerned there are only temperature gauges on that. There is a tap for venting and when I tested that there was no air coming out, only water.

There is a possibility that the red tank has failed (It feels heavier than it was - as though now full of water) so I will ask the plumber to come back and check that out.

Grallert · February 12

That's a good start. Please keep us posted I am very curious about your system, they are not common here in the US.

Log-Burning Boiler and "Closed System" Pressure Problem

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