Hydrogen in one radiator

[StillGame]

Closed heating system, approx 14 years old with oil fired boiler, feeding around 18 radiators over 2 floors. One small radiator nearest the boiler and downstairs repeatedly fills up with hydrogen over a period of about 4 weeks. Hydrogen is suspected as it can be ignited and there is no smell. System was flushed and treated with inhibitor last year, and no leak is apparent (including inside the boiler as the engineer has tested it). Litmus paper indicates the water is on the acidic side - there are some minor signs of corrosion around some of the radiator connections but nothing extensive. The bad radiator can feel perfectly fine for a week or two and some time during operation there is a sound of air gurgling through the system - but always ends up in this same radiator. Is it just corrosion across all the radiators, but always ending up in this one radiator? One engineer reversed the pump direction when it was flushed, as the feed was flowing the wrong way, yet the problem is always in the same radiator.

 

[Chuck]

The pH should typically be in the range 6.5–8.5. If it's more acidic than 6.5 you'll get corrosion and hydrogen evolution.

It's quite normal for air/hydrogen to accumulate preferentially in one radiator. It often seems to migrate to a point with relatively low pressure and/or high temperature, e.g. a tall towel rail in an upstairs bathroom.

How to: control corrosion in central heating systems

I want to know how to prevent corrosion of central heating system metals such as copper, aluminium, steel and more

www.sentinelprotects.com

 

[StillGame]

Will adding more corrosion inhibitor reduce the acidity? Why would it be so acidic when it was flushed clean and inhibitor was added last year?

 

[Chuck]

Will adding more corrosion inhibitor reduce the acidity? Why would it be so acidic when it was flushed clean and inhibitor was added last year?

What's the pH of the local water supply?

What chemicals did you use to flush it? Did you follow the manufacturer's instructions to the letter?

After cleaning, did you flush with clean water at least twice and monitor progress by checking the pH at each stage?

Did you add the correct amount of inhibitor?

Corrosion inhibitors do usually reduce the pH but they aren't a substitute for neutraliser if that's what's needed.

Another approach is to test a sample of the system water. Use a kit from the same manufacturer as the inhibitor you've been using. The test comes back from the lab with an analysis of what's wrong and recommendations to fix. They cost £30 – £60 from a plumbers merchant depending on how sophisticated the analysis is. Not free, and shouldn't be needed if you follow the instructions on the cleaner and inhibitor correctly. But blindly pouring loads of inhibitor into a system that may or may not need it isn't cheap either.

 

[StillGame]

Local water is close to pH 7. A professional did the flush and did spend all day and used Norstrom chemicals and did flush with water (nor sure if pH was monitored) and added inhibitor at the end.

Thanks for the advice: I've ordered a water test kit.