The boiler itself was in excellent condition. It was only three years old, still under manufacturer warranty, and the customer had reported no faults with heating or hot water.
But during this routine annual boiler service in Hanwell W7, the magnetic filter told a very different story. When it was cleaned, it revealed a heavy build-up of black magnetite sludge. A heating water sample was also taken, and the water was so dark it barely looked like clean system water at all.
Job Snapshot
| Item | Detail |
|---|---|
| Customer type | Homeowner |
| Location | Hanwell W7 |
| Existing boiler | Vaillant ecoTEC Plus system boiler, approx. 3 years old |
| System type | Sealed heating system with vented hot water cylinder |
| Additional protection | Magnetic filter cleaned; power flush and inhibitor treatment recommended |
| Warranty | Boiler still within manufacturer’s warranty period, with annual servicing required to maintain it |
| Serviced by | Vincent O’Gara, Ealing Boiler Services |
The Problem
This was a routine manufacturer-recommended annual service, not a callout for a fault. The customer had not reported any issues with heating or hot water, and on the surface, everything looked fine.
I removed the casing, checked the appliance internally for leaks, corrosion, heat distress and loose connections, and found no problems. The boiler was clean, well-kept and in excellent condition throughout.
The issue was not inside the boiler itself. It was in the heating system water.
As part of the service, I checked the magnetic filter, which is designed to collect debris circulating around the radiators and pipework. When the filter was removed and opened, I found a significant amount of black magnetite sludge. This is a clear sign of corrosion within the wider heating system, even though the boiler itself was still showing no signs of damage.
A water sample taken after the filter clean confirmed the concern. The sample came out almost black. An ADEY ProCheck test showed poor inhibitor levels and heavy contamination, meaning the water inside the heating system was no longer properly protected against corrosion.
Left untreated, contaminated heating water can reduce system efficiency, put extra strain on pumps, clog valves and shorten the lifespan of the boiler and wider heating system.
My Solution
With the appliance itself in good condition, the service focused on checking everything properly rather than assuming the boiler was the problem.
I tested the electrical supply using a calibrated multimeter, confirming the correct voltage, polarity and earth continuity. I checked the expansion vessel for signs of corrosion or leaks, inspected the full flue run internally and externally, and confirmed the condensate pipe and pressure relief discharge pipe were both terminating safely.
I also carried out a full combustion analysis using a calibrated flue gas analyser in the manufacturer’s test mode. This confirmed correct CO₂ levels and safe, efficient combustion, with no adjustment needed.
Once the magnetic filter had been cleaned and refitted, I reassembled the boiler, tested it for safe operation, and confirmed both the heating and hot water were working correctly.
The Result
Every safety check on the appliance itself passed. The electrics, gas pressure, combustion, flue and expansion vessel were all sound.
The only issue found was the condition of the heating system water, and the ADEY ProCheck result made that impossible to ignore.
I completed the service record in the Benchmark book, issued a digital service certificate, and talked the customer through exactly what the water test showed.
My recommendation was a professional power flush, fresh system water with the correct concentration of corrosion inhibitor, a follow-up water test to confirm the improvement, and ongoing annual filter cleaning to help keep the system protected.
The boiler passed its annual service and remains protected under warranty. More importantly, the customer now has clear evidence that the heating system water needs attention before it causes damage in the future.
Got a Similar Problem in Ealing or West London?
A clean boiler service certificate does not always mean the whole heating system is in perfect condition. The boiler can be working safely while the water running through the system is slowly causing corrosion and wear.
At Ealing Boiler Services, we check the magnetic filter and heating water quality as part of our annual boiler servicing. This helps catch problems early, before they lead to breakdowns, poor efficiency or a shortened boiler lifespan.
We cover Ealing, Hanwell, Chiswick, Brentford and the surrounding West London area. Every boiler service includes a full safety check, clear advice, a digital certificate, and honest feedback on what we find.
Call Ealing Boiler Services: 02081234567
Visit: ealingboilerservices.co.uk
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