The boiler kept losing pressure, but there was no puddle beneath it. On our first visit to Granville Road in Childs Hill, NW2, we traced the water loss to a leak inside the Worcester Bosch Greenstar 42CDi Classic ErP. TNG Services Ltd returned to replace the main heat exchanger and test that the boiler held pressure and provided heating and hot water.

Where was the boiler losing water?

The boiler was displaying an E9 fault and repeatedly losing heating system pressure. We checked the expansion vessel, recharged it to 1.1 bar during the visit and inspected the accessible heating pipework for signs of leaks.

We found a broken filling-loop key and a faulty filling mechanism. Replacing the filling-loop assembly addressed that fault, but the pressure kept dropping. Further testing traced the water loss to the main heat exchanger: heating system water was escaping into the condensate drain instead of dripping visibly beneath the boiler.

See our original Worcester Bosch E9 and pressure loss investigation for the full diagnosis.

Replacing the main heat exchanger

After discussing the cost of the repair and the age of the boiler, the customer chose a refurbished main heat exchanger for this job. We returned to fit it, giving the customer a way to repair the existing boiler without replacing the whole appliance.

Heating and hot water restored

After fitting the replacement heat exchanger, we tested the boiler. We confirmed that:

• The heating system held pressure.
• The heating worked correctly.
• The hot water worked correctly.

Boiler losing pressure without a visible leak?

In this case, the water escaped through the condensate drain, so there was no obvious drip beneath the boiler. Repeatedly topping up the system does not fix the cause of pressure loss. An investigation can establish where the water is going and whether a repair is practical.

We provide boiler fault finding, repairs and boiler servicing across Childs Hill, Cricklewood, North London, Stevenage and Hertfordshire.