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Hot water heating system leak diagnosis & repair; here we explain how to determine that a hot water heating system is in fact leaking, and second we describe how to find the location of hidden leaks in or on heating boilers, hot water heat piping, baseboards, radiators, convectors, or radiant heat floors or ceilings.
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The photograph at page top shows that a heating convector recessed into the wall had been leaking into the wall structure for a long time. The leak was discovered by removing the convector cover for direct inspection. We could also see evidence of this leak by inspecting for water stains or damage at the building sills in the basement below.
At above/left our photo shows a severe leak at an air bleed fitting on a hot water heating baseboard line that was eventually separated by freezing and frost-push.
While freezing can burst piping and cause serious leaks in buildings, a bad solder joint may be dripping into a wall, ceiling or floor for quite some time before it is detected. Although the leakage rate in a hot water heating piping system increases when the system is hot and in use (and at higher operating pressure than when cold), much of the water leaking out of the piping evaporates.on the hot piping surface.
It is important to recognize and accurately report the significance of rust like this on any heating boiler. We continue to add to and update this text as new details are provided. Contact us to suggest text changes and additions and, if you wish, to receive online listing and credit for that contribution.
Most modern heating boilers include an automatic water makeup valve that combines pressure reduction (to 12 psi cold on the boiler side of the valve) with automatically makeup water if the boiler pressure drops below that point. Details are at WATER FEEDER VALVES, HYDRONIC BOILER.
How Do I Know if my Heating Boiler is Leaking?
A small water leak in a hot water heating system (hydronic heat) will eventually cause pressure loss in the system, but you may never notice this problem. Leaks on hot water heating systems are likely to occur, or to leak more rapidly when the heating system is hot (at higher pressure) than when it's cool.
The pressure drop from a small heating system water leak may be occurring over a long time, months or longer, and because the leaked-water may simply dry out on the hot heating piping where it is occurring you may never see a wet spot on a floor, wall, or ceiling below the leak.
How Do I Find Leaks on Hot Water Heating Systems?
To detect a small leak in a hydronic heating system we have had some success with these measures:
Look particularly closely where there are probably tubing connectors such as at manifolds and at the start and ends of tubing runs.
Look on floors and other building surfaces, not just at the piping itself. Our photo (left) shows the results of a dripping boiler drain.
A large water leak in a hot water heating system will usually show up quickly as a puddle, a ceiling, wall, or floor stain, or worse, as mineral clogging and damage to the boiler itself, caused by the excessive level of minerals in the constantly-added make-up water (if your area's water supply is high in mineral content).
Readers should also see BOILER LEAKS CORROSION STAINS where we provide a catalog of places where leaks often occur on hot water heating systems. This article series answers most questions about central hot water heating system troubleshooting, inspection, diagnosis, and repairs.
We describe how to inspect, troubleshoot and repair heating and air conditioning systems to inform home owners, buyers, and home inspectors of common heating system defects.
Reader Question: heating boiler expansion tank pressure drops to zero - we keep adding water.
We have the Weil-McLain boiler in floor heating system... re Expansion Tank... every 4-7 days the pressure goes down to zero (from 10 – 20 psi)... we have a hose connected that we turn on both valves and let the water go into the tank to bring the pressure up to 10-20 psi..but still will not hold...what is the problem? and what if we do not fill with water and leave at zero? advise please. - B.A. Watford, Ontario
Reply: look for a leak in the heating system
I may not understand your question properly, and an expert onsite inspection usually reveals important additional information. Some photos or a sketch may help me comment further - but from what I can make out you are talking about a hot water heating system and the expansion tank connected to the heating system piping and boiler.
The expansion tank's job is to absorb the initial pressure increase in the system as water heats up -- thus to avoid improper heating water spilling at the pressure/temperature relief valve. On an older steel bladderless heating system expansion tank installation, the tank eventually becomes waterlogged (air is absorbed into the heating water) and then the relief valve drips. The "fix" is to completely drain the tank, allowing air to enter it. When the system is turned back on and heating water is forced back into the tank, at system COLD pressures, the tank will have some water and some air inside it and the heating system pressure will be around 12 psi.
On occasion there is an air leak at the top of an expansion tank - but if that's the case you'd eventually see rust or water dripping down the tank when it becomes waterlogged. So I suspect that there is a water leak elsewhere.
I'm unclear where you are measuring pressure. Expansion tanks don't usually have a pressure gauge attached, but as the tank and heating piping and boiler are all connected the boiler pressure gauge is approximately reflecting the system pressure. I say approximately because the precise system pressure varies at different locations, for example it will be a bit lower at the highest point in the piping system than at the lowest point of the boiler.
Now you should not be having to add water to your heating system. Its pressure is really dropping to zero (as opposed to a gauge problem for example) then there is probably a leak somewhere that you need to find and fix.
If you have an in-floor radiant heat system the leak could be hidden below a floor slab - a condition we find by using an infra red scanner or by shutting off the water supply to the boiler and watching for a pressure drop.
I think that's the direction you need to investigate.
If you have not already read it see BOILER LEAKS CORROSION STAINS
Also see CHEMICAL TREATMENTS, Boiler for a discussion of leak-stop products.
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