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Glow-Worm Boiler F73 Fault Code

The Glow-Worm fault code F73 relates to the pump not being shown as active and here we have Q & A or require an engineer for an emergency boiler repair.


The Glow-Worm Boiler Fault Code F73 Error Common Q & A

Just below, we have a list of common questions relating to the F73 fault code on the Glow-Worm Boiler.

Glow-Worm boiler error code F73
  • What does the F73 fault code mean on my Glow-Worm boiler?
  • What does the pump do on my Glow-Worm boiler?
  • Will I be able to fix the F73 fault on a DIY basis?
  • What does my heating engineer need to do to fix the F73 fault code?
  • If heating sludge is the problem, is there a fix?
  • How can my boiler engineer determine what’s wrong with the pump?
  • If I need a new heating pump, how much is it going to cost to fit?
  • My pump is running, so what’s the problem?
  • My boiler engineer has tested the PCB and thinks that’s the problem, is this right?
  • If I need to replace the PCB on my Glow-Worm boiler, how much will it cost?

What does the F73 fault code mean on my Glow-Worm boiler

If you’re seeing the F73 fault code on your Glow-Worm boiler, the problem is due to the pump not being shown as active.

Your boiler is controlled by the printed circuit board (PCB). This gives and receives signals from sensors, as well as important components like the pump.

In this case, the pump should be active, but it’s not. Your boiler locks out to protect internal components from damage. Continued operation when the boiler has a fault could lead to a boiler overheating, and expensive repair bills.

What does the pump do on my Glow-Worm boiler

The pump circulates water around your heating system, as well as to taps and showers. Water passes through the heat exchanger, and the pump pushes this around the heating system. Naturally, this water cools down as it travels around the system, so runs on a continuous circuit, travelling back to the boiler to be reheated.

If the pump isn’t active, water won’t be flowing around your heating system. There might be a small let-by, whereby the flow thermistor (the sensor on the pipe where water leaves the boiler), and that will show that temperature is increasing. However, the sensor on the return pipe (where water returns to the boiler to be heated), is going to show a huge differential in temperature, as hot water isn’t reaching that far.

In this case, the differential is so big, the PCB doesn’t see that the pump is active. That’s going to cause water to stay in the heat exchanger. If it overheats, it could crack the heat exchanger, causing expensive repair bills.

Will I be able to fix the F73 fault on a DIY basis

The F73 fault code fix, is going to require the boiler to be taken apart. Legally, you’d need to be Gas Safe registered to fix a gas appliance like your boiler.

So, call an emergency boiler repair company. They’ll have Gas Safe registered repair engineers that will have had experience with the F73 fault code on Glow-Worm boilers. Once they’ve managed to fix the problem, they’ll be able to reset your boiler, which will clear the F73 error code from the display panel.

What does my heating engineer need to do to fix the F73 fault code

The first thing for your heating repair company to do, is determine whether the pump is working. Just because the PCB is showing that the pump isn’t active, doesn’t mean that’s the case. The error could just as easily be with the PCB.

Instead of a pump error, it could be that the PCB has a fault whereby it’s not receiving the correct signals from the pump.

It will become immediately apparent to your boiler engineer whether the pump is working. Firstly, when a pump is working, it’s going to vibrate. And, if it’s circulating water around the heating system, both the flow and return pipes will be warm, with only a little differential between the temperature of the two pipes.

If the pump isn’t active, they’ll need to determine what’s caused the pump to stop working.

How can my boiler engineer determine what’s wrong with the pump

Before replacing or repairing the pump, they’ll need to check all wires and connections to it. If even one of these are loose or damaged, that’s going to affect the signals being passed between the pump and the PCB.

To test your pump and all its wiring and connections, your boiler engineer will need to use a multi-meter. This helps them determine at which point in the circuit, there is a break.

For minor connection and wiring issues, small repairs can be made. But, in some cases whereby the pump isn’t functioning, a replacement is going to be needed to fix the F73 fault code on your Glow-Worm boiler.

If heating sludge is the problem, is there a fix

Blockages can put excess strain on your boiler’s pump. Whether that’s air locks or heating sludge, they need to be removed. In extreme cases, air locks and heating sludge blockages could be so bad, that they stop the pump from working completely.

If your pump has power and there’s no problem with the PCB, have your engineer inspect your pump for heating sludge. This can be manually removed to help the pump circulate water. And, once the pump has been refitted, they can bleed air locks from the pump, using the bleed screw.

If I need a new heating pump, how much is it going to cost to fit

Replacing the pump on your boiler is likely to cost around £250. That price includes parts (from a top pump brand such as Grundfos), and labour. Typically, you should expect the fault-finding process and the new pump installation to be completed in less than a day.

My pump is running, so what’s the problem

The pump isn’t being shown as active, but that doesn’t mean that this is the case. The problem could be with the wiring to/from the pump, or the PCB.

As your boiler engineer did with the pump, they’ll need to use a multi-meter to determine where there is a break in the circuit.

If there’s an issue with wiring and connections on the pump, the pump can’t give the signal to the PCB to tell it that it’s operating.

And, if there’s an issue with the wiring and connections on the pump, the PCB won’t be receiving the signal from the pump, to say that it is operating.

Your boiler engineer will be able to secure connections and repair minor wiring damage.

My boiler engineer has tested the PCB and thinks that’s the problem, is this right

Not all problems relating to the F73 fault code are simple fixes. If your boiler engineer has tested the PCB on your Glow-Worm boiler and it’s not responding, there’s a chance you might need a replacement.

Typically, if your boiler’s PCB isn’t working, you’ll have noticed your boiler working intermittently. This might mean sporadic operation such as it cycling on and off at random, or the display panel going blank on occasion.

As the PCB communicates with all electronic parts in your boiler, once it fails, your boiler is going to work sporadically, or not at all. And, as this is the part that determines which fault code should be displayed, if it’s faulty, the fault code being displayed could be incorrect.

If I need to replace the PCB on my Glow-Worm boiler, how much will it cost

The PCB on your boiler is the most expensive part to replace. Typically, you should expect to pay somewhere in the region of £400-500.

And, with repairs that are this expensive, you should consider getting some quotes for a new installation. If the PCB has already failed, it’s likely other parts will fail soon. And it makes no sense to invest large amounts of cash into a failing boiler.

Your boiler engineer will be able to assess the current condition of your boiler’s most expensive components, such as the heat exchanger, pump, PCB and fan. If these parts are excessively worn, a replacement boiler is likely to be a better option than a repair.

Other Glow Worm boiler issues

For more boiler issues regarding the Glow Worm then please visit the Glow Worm Boiler Problems And Cures page.