In 2017 the owner of the Walker House in Carmel-by-the-Sea, CA. set about mapping the house’s radiant heating system, which dated from the house’s 1951 construction. FLIR (“Forward-Looking Infrared) thermal imaging was used, which gave an understanding of the system’s piping layout. When a leak developed in 2019, this advance work proved very useful.
Andy Runnoe of Runnoe Construction, who worked with the owners, describes the fall 2019 activity:
This home was built in the early 1950’s and has a radiant heat system, run through 1/2” copper waterlines imbedded in the concrete floor. A leak developed under one of the showers, and the automatic fill valve could not keep up with the leak, overheating the pump. It was identified by injecting Helium into the system and running the detector throughout the house.
Due to the location (under a shower pan), it was preferable to try to fix the leak without removing the shower and replacing it.
The Material used was Silver King SBSL, Liquid Boiler Stop Leak with Anti Foam Silicone SK-24*, manufactured by Silver King Manufacturing (www.silverkingmfg.com / 1-800-638-0237). After consulting the manufacturer, we decided to use twice the recommended amount. Try to determine the amount of water in your system by calculating the linear feet of pipe in your system. We used thermal imaging to determine the length of pipe in the system.
The following is the methodology we used, along with steps that must be taken.
- Bring system to full water capacity.
- System must be brought up to its normal heated temperature. Water must be hot. 140 F recommended.
- Turn off the automatic fill valve, isolating system. Try not to introduce any more water into the system. Open any zone valves in the system.
- Add Silver King at boiler by some means, depending on the configuration of your system. We pumped it in at a hose bib on the boiler normally used to drain the system.
- Run system for two to three hours under pressure. Be careful that the system does not run dry. It is alright for the product to run through the boiler.
- Turn system off for 12-24 hours. We let it sit overnight, about 16 hours.
- Restart the system and check to see if the fill valve is replacing any volume of water.
Note that due to cooling and heating, a slight amount of water may need to be made up. It should not amount to more than a gallon or two, depending on the size of your system.
If necessary, repeat procedure. It worked for us on the first try.
A similar stop-leak project
The following is taken from the Building Conservancy’s Bulletin, spring 1998, by Gerald Lee Morosco, AIA, describing a stop-leak application at another Usonian house:
In terms of a “band-aid” solution, many homeowners have reported of success through the introduction of liquid stop leak products. Introduced into the systems’ water supply, these products contain microscopic silicones which accumulate in and plug tiny holes and cracks. Hercules Chemical Company of Passaic, New Jersey (201.778.5000) manufactures two such products: Hercules Boiler Liquid and Hercules Base Hit II*. These products are available through plumbing supply houses and are known to most plumbers. We strongly recommend that you consult with a qualified plumber familiar with hydronic heating systems before the use of these products. The manufacturer’s application instructions should be followed carefully with special attention given not to exceed the recommended dosages of these products in your heating system. If you are not familiar with the service history of your heating system, it should be determined that similar products have not been previously introduced into the system.
This winter,  following two incremental applications of Boiler Liquid, one original homeowner reported to me that the heat in her 1953 Usonian was more uniform and generally warmer than it ever had been. This suggests that many small leaks, which had developed over time, were remedied by the treatment. As of this writing, I know of one other home, in which such an application has arrested further leaking for two years.
Hercules products are still manufactured in 2023. Roland Reisley noted recently [link to Roland’s article], “Hercules Boiler Liquid* can sometimes seal small leaks for quite a while.”
* Please Note: The provision of this information or mention of a specific product or products does not constitute endorsement, recommendation, preference or approval by the Conservancy. It provided only as a record of activities and as a starting point for further research by other building stewards.
Radiant Heating 101 - Introduction Page
Posted April 3, 2023