Plumbing the depths

Our Worcester Bosch 440 High Capacity boiler stopped working this morning, just after lunch. Code D5 means the condensate pump isn't functioning correctly, either due to a blocked pipe or some issue with the pump itself. This pump has a reservoir that collects the condensation from the primary heat exchanger (gas flame), then periodically discharges itself via a small pipe that ends in a drain outside the house.

The Worcester Bosch 440 High Capacity installation manual is pretty comprehensive and well written and includes a good parts lost, various exploded views and installation / replacement instructions.

The HC models have a "heat store" (item #44) ie a mini hot water tank (45 litres / 10 gallons), as well as a larger water-to-water heat exchanger (item #17) that allegedly allows more than one bath or shower to be used simultaneously. Consequently, it's a floor standing device, rather than the more normal wall mounted installation.

This thing is 10 years old now, so perhaps the pump is getting a bit long in the tooth. I've also bought a replacement water-to-water heat exchanger (item #17), as I'm not convinced it's working quite as it used to. Finally, I've got an auto bleed valve for the heatstore (item #42), as the original shows signs of leakage. They all weep to some degree but as they are pretty cheap, it's something to be done when the thing is drained down and in pieces.

Let's go. The control panel and bladder (the orange pressurised tank) both swing out of the way on hinges:

The pump is the off white box at top left with the clear-ish hose emerging on the top. When powered up, it shows a constant red LED indicating a problem "not emptying" issue.

A bit of a fiddle to extract but here's what you find. The lid just lifts off. There's a float (back left) with a Hall sensor to detect when the tank is full. Then there's a tiny pump hidden under the removable cover at the front, driven contactlessly through the plastic body.

The 240V power and the level switch (or possibly status output) come to the cotrol board through this array of cable grips.

Sensor / status input to the control board:

240V input, including protective earth. The cowboy plumbers who originally installed the boiler had barely trapped any of the conductor under the clamp. It's a good thing they had done their "competent person" training that allows them to do electrical installation work. I replaced the entire cable and used ferrule crimps.

Here's the original shitty mains wiring, although it's hard to see what is happening here. Take my word for it though - it's not pretty.

The old and new pumps are absolutely identical. Even though their date codes differ by almost a decade, the version number is the same and the manufacturer's name is show on the PCBA (Xylem).

Here's the puny motor.

It has a special connector for the Glow Worm control board.

The Glow Worm cable actually has 3 connections but one is just live with a resistor. Cut them off and you have the same terminations.

I'll be swapping out this heat exchanger while I'm at it.

And the auto bleeder that sits on top of the heat store. Getting it off wasn't easy, as the thread was stiff and spanner access was limited.

All done. Connected back up, refilled and powered up. Result.