TNG Services Ltd attended an emergency boiler repair enquiry on Granville Road in Childs Hill, near Cricklewood, North West London NW2. The customer’s Worcester Bosch Greenstar 42CDi Classic ErP was displaying an E9 fault and had lost its heating-system pressure.
A detailed investigation identified a faulty filling mechanism and an internal leak in the boiler’s main heat exchanger.
Repair update: The filling-loop assembly has been replaced. The main heat exchanger replacement remains outstanding, and final testing will take place after that repair is completed.
What does the Worcester Bosch E9 fault mean?
On this boiler, the E9 fault indicates that the safety temperature limiter in the central heating flow has tripped, causing a protective shutdown.
Low system pressure or inadequate water circulation can contribute to this fault. However, the fault code alone does not identify the cause — inspection and testing are required.
Expansion vessel checked and recharged
Following the E9 fault, we checked the expansion vessel and recharged its air pressure to 1.1 bar.
The heating system was refilled, but the boiler continued losing water pressure. This showed that further investigation was needed.
Checking the property and exposed heating pipework
We checked throughout the property and inspected the exposed heating pipework for visible drips, leaks and signs of water damage.
No visible external leaks were found in the areas inspected. We then continued the investigation inside the boiler to establish where the water was escaping.
Faulty filling-loop assembly replaced
During the inspection, the filling-loop key was found broken, leaving the filling mechanism stuck in an open position.
The filling-loop assembly was replaced, and the system was refilled. However, the boiler continued losing pressure, confirming that another fault remained.
Main heat exchanger leak found
Further testing identified an internal leak in the boiler’s main heat exchanger.
Heating-system water was escaping through the heat exchanger and passing into the condensate trap and drain. This explained why the boiler was losing pressure without a visible leak beneath the appliance or around the exposed heating pipework.
Condensate is not automatically evidence of a fault. Condensate drainage is normal when a condensing boiler operates. In this case, our investigation identified heating-system water leaking into that drainage route.
Replacement heat exchanger agreed
The faulty main heat exchanger requires replacement.
Considering the boiler’s age and the high cost of a new heat exchanger, we discussed a lower-cost refurbished replacement with the customer. The customer agreed to this option, and we are currently awaiting the replacement part.
Once the part arrives, we will return to complete the repair and carry out final testing to confirm that the boiler holds pressure and operates correctly.
The investigation is complete, but the heat exchanger replacement remains outstanding.
Check the expansion vessel, accessible pipework and internal boiler components.
Replace the faulty assembly and identify the separate internal heat exchanger leak.
Complete the heat exchanger replacement and final testing. This stage remains pending.
Why repeated boiler pressure loss needs investigation
Repeatedly topping up a boiler does not fix the underlying reason for water loss.
This investigation highlights why checks may need to include the expansion vessel, filling mechanism, accessible heating pipework and internal boiler components. An internal heat exchanger leak can allow water to escape through the condensate drain without leaving an obvious puddle.
If your Worcester Bosch boiler repeatedly loses pressure or displays an E9 fault, arrange an assessment by a Gas Safe registered engineer.
Boiler fault finding in Childs Hill and Cricklewood NW2
Contact TNG Services Ltd to discuss boiler fault finding and repairs in Childs Hill, Cricklewood and the surrounding North West London area. For routine maintenance, explore our boiler servicing services.
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