Glow-Worm Boiler F.71 Fault Code
The Glow-Worm fault code F.71 relates to the flow return sensor and here we have Q & A or require an engineer for an emergency boiler repair.
The Glow-Worm Boiler Fault Code F.71 Error Common Q & A
Just below, we have a list of common questions relating to the F.71 fault code on the Glow-Worm Boiler.
- What does the F.71 fault code mean on my Glow-Worm boiler?
- What are the flow and return temperature sensors on my Glow-Worm boiler?
- Can the F.71 fault code be fixed on a DIY basis?
- How can the F.71 fault code be fixed?
- I’ve noticed other fault codes being displayed, is the problem limited to the temperature sensors?
- How will my boiler engineer know if heating sludge is causing issues?
- Can the pump speed be adjusted on my Glow-Worm boiler?
- How will my boiler engineer know if the pump on my boiler is defective?
- How much does it cost to replace a pump on a Glow-Worm boiler?
- My boiler engineer still can’t find the problem, are there any other potential culprits?
- My PCB needs replacing, how much should I expect to pay for a new one?
What does the F.71 fault code mean on my Glow-Worm boiler
If your boiler develops a problem, the printed circuit board (PCB) is going to notice. It’s the PCB that gives and receives signals to all electronic components, as well as monitoring all sensors.
Once it notices a problem, it tries to display a fault code that is specific to the problem at hand, in this case, F.71. The idea behind these fault codes is to give your boiler repair company an indication of what the problem is.
That’s going to mean that they spend less time diagnosing the fault, and your repair bill is much lower than it would be otherwise.
The F.71 fault code relates to a flow/return sensor issue.
What are the flow and return temperature sensors on my Glow-Worm boiler
Flow and return temperature sensors monitor water temperature at different points of your heating system.
The flow sensor monitors hot water that’s leaving the boiler. The flow pipe is the hottest pipe on the boiler.
The return sensor monitors water that’s travelled round your heating system, it’s returning to the boiler via the return pipe, ready to be re-heated. This pipe will be slightly cooler than the flow pipe.
These sensors are put in place to check that water temperature isn’t too hot when water leaves the boiler. The PCB also monitors the temperature differential between the two sensors. Once it goes beyond a certain point (usually, a 40-degree differential), it locks out in case there’s a problem.
Can the F.71 fault code be fixed on a DIY basis
You shouldn’t work on gas appliances, unless you are qualified with Gas Safe. So, you’ll need to call a Gas Safe registered boiler repair engineer to fix the problem.
They’ll isolate the issue, fix the problem and then reset your boiler. This will clear the F.71 fault code.
How can the F.71 fault code be fixed
It’s most likely that the sensors on your boiler are faulty. So, your boiler engineer needs to first, check them using a multi-meter. This will determine that each sensor is getting the correct amount of electrical power.
If the flow and return temperature sensors aren’t getting power, the only option here, is to replace them.
When these sensors are faulty, it’s likely they are giving the PCB a constant temperature reading, rather than one that’s going up and down inline with your demand for heat and hot water.
The other cause could be that the temperature sensors have been fitted incorrectly or are on the wrong pipes. This is going to be immediately obvious to your boiler engineer. And, if this is the case, it’s going to be a cheap and simple fix.
I’ve noticed other fault codes being displayed, is the problem limited to the temperature sensors
There are a range of other fault codes that are relevant to Glow-Worm boilers, that are linked to temperature sensing issues. However, not all are related to faulty sensors.
If you’ve noticed other fault codes being displayed that relate to temperature sensing issues, it might be that flow is restricted for a range of reasons. When flow is restricted, your boiler might have issues with:
- Water overheating
- The return pipe being too cold
And, that’s going to mean that you have problems such as:
- Radiators not heating up quickly enough
- Radiators being cold at the bottom, but warm-hot at the top
If this is the case, the problem is unlikely to be with the temperature sensors in your boiler, but instead, flow.
Flow restrictions in modern boilers are usually due to:
- Sludge in the heating pump, heat exchanger and radiators
- Incorrect pump speed setting
- Faulty pump
How will my boiler engineer know if heating sludge is causing issues
If you have never had your system flushed, it’s not dosed with inhibitor and you don’t have a magnetic system filter installed, there’s a good chance that heating sludge is what’s causing the issues with your boiler.
Central heating sludge is a combination of rust that breaks off from radiators, towel rails and the inside of copper pipework.
This can block lots of boiler components, leading to expensive damage, and even cause radiators not to heat up correctly. It can also lead to a large temperature differential between the flow and return temperature sensors.
Luckily, there is a fix. You’ll want to get your engineer to manually clean out the pump, and then hot flush your system using chemicals. This will get rid of most of the heating sludge in the system.
Once they’ve done this, you need to stop this happening again. The best thing to do, is dose the system with central heating inhibitor, and then fit a magnetic system filter. It’s the inhibitor that breaks down sludge, and it’s the filter that then catches it.
Can the pump speed be adjusted on my Glow-Worm boiler
If sludge isn’t causing the circulation issue on your Glow-Worm boiler, your engineer will want to look at the pump. Modern pumps (such as Grundfos), have three speed settings.
If you have a large property, it’s likely you’ll need to have a pump running on the highest speed setting. A speed setting lower than this is going to mean that water doesn’t travel around the heating system quickly enough. When this is the case, water might overheat in the heat exchanger, but also, by the time it reaches the return pipe, it’s going to be too cold.
Your engineer will be able to adjust the pump’s speed, to rectify the problem.
How will my boiler engineer know if the pump on my boiler is defective
Without a working pump, your heating and hot water isn’t going to work correctly either.
If your boiler engineer has checked the pump for blockages (such as heating sludge) and bled the pump of air to no avail, they’ll need to check the pump’s installation and running capabilities.
The first thing to check, is that the pump is installed horizontally. If it’s not installed horizontally, this is going to wear out the pump’s shaft and bearings. Eventually, it’s going to become incredibly noisy, and then stop working completely.
If the pump’s installation looks correct, and it’s free of sludge, they’ll need to test it for power. They can do this by using a multi-meter. If it doesn’t have power, they’ll need to re-secure wiring/connections that have come loose. And, if that doesn’t work, the pump will need to be replaced.
How much does it cost to replace a pump on a Glow-Worm boiler
A typical pump replacement is going to cost somewhere in the region of £300. That includes labour and all parts, including a top-quality pump, from a well-known brand such as Grundfos.
My boiler engineer still can’t find the problem, are there any other potential culprits
If you’ve been seeing multiple fault codes being displayed, and your engineer can’t find the problem, they’ll need to check the PCB.
It’s the PCB that controls all electronic components, and sensors. So, if it’s faulty, it could be giving or receiving the wrong signals. For instance, it could be monitoring incorrect temperatures, even though the flow and return sensors are showing temperature readings that are in tolerance.
Like the pump, your boiler engineer will be able to check all wires and connections, re-securing them where necessary. They can then test for power using their multi-meter.
My PCB needs replacing, how much should I expect to pay for a new one
If your PCB is faulty, a new one is going to be needed. Unfortunately, this is the most expensive part to replace on a boiler. You should expect to pay around £450-500, including parts and labour.
Other Glow Worm boiler issues
For more boiler issues regarding the Glow Worm then please visit the Glow Worm Boiler Problems And Cures page.