My trusty old Worcester Heatslave 2+ started kettling noisily recently. Black oxide probably came off the cast iron boiler sides and deposited at the bottom of the boiler above the burner.
The primary circuit was last flushed with acid about 20 years ago, so not surprising some corrosion has taken place.
A quick call to my gas engineer who pointed out that most of the proprietary descaling and sludge removal chemicals sold in liquid form are neutral pH these days and don't actually dissolve sludge, but break it down into suspension prior to power flushing.
As I needed to dissolve it, and not having a power flushing unit, I was recommended citric acid as a suitable chemical to use. The sludge, which is dense, was not being washed out of the system from any drain points by the pressure of refill water alone.
Two kilogrammes of citric acid, dissolved in warm water, did the trick. Added via the primary system header tank it dissolved all the sludge in about two hours with the pump and boiler running. Drain water showed iron in solution as green and orange clear liquid, which I ran until it became colourless. I neutralised the system with 200g of bicarbonate, drained again and refilled.
The kettling and popping completely disappeared.
This could hardly have been more straighforward, made all the more so by having a simple, if somewhat inefficient by today's standards, boiler.
The primary circuit was last flushed with acid about 20 years ago, so not surprising some corrosion has taken place.
A quick call to my gas engineer who pointed out that most of the proprietary descaling and sludge removal chemicals sold in liquid form are neutral pH these days and don't actually dissolve sludge, but break it down into suspension prior to power flushing.
As I needed to dissolve it, and not having a power flushing unit, I was recommended citric acid as a suitable chemical to use. The sludge, which is dense, was not being washed out of the system from any drain points by the pressure of refill water alone.
Two kilogrammes of citric acid, dissolved in warm water, did the trick. Added via the primary system header tank it dissolved all the sludge in about two hours with the pump and boiler running. Drain water showed iron in solution as green and orange clear liquid, which I ran until it became colourless. I neutralised the system with 200g of bicarbonate, drained again and refilled.
The kettling and popping completely disappeared.
This could hardly have been more straighforward, made all the more so by having a simple, if somewhat inefficient by today's standards, boiler.
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