Ferroli F37 fault codewhat it means and how to fix it
System water pressure is outside the correct range. Because this is an F code it clears by itself once you top the system back up.
Before you start
What does the gauge read right now?
The right answer depends on what you can see. Pick the one that matches.
Choose the option on the left that matches what your appliance is doing, and the answer for that case appears here.
Below 1 bar
Genuinely low. Top up to 1.2 bar and the fault will clear itself without a reset.
Refill through the filling loop and note the date for future reference.
Between 1 and 1.5 bar, but the fault is still showing
The pressure is correct and the appliance disagrees, which points at the pressure switch or transducer rather than at the water. Ferroli list a damaged switch as a cause of this code for exactly this reason.
Book an engineer. It is not an expensive part, but it is inside the case and therefore not householder work.
Above 2.5 bar
Overfilled, or the expansion vessel has failed. The code covers incorrect pressure in either direction, not only low.
Bleed a little water from a radiator into a container to bring it back to 1.2 bar cold. If it climbs again as soon as the heating runs, the expansion vessel needs attention.
What F37 means
Ferroli describe F37 as incorrect system water pressure, and the wording matters — the manual lists both low pressure and a damaged pressure switch as causes, so the code covers the measurement as well as the thing being measured. Being an F-prefix fault, it is a temporary shutdown that resets automatically the moment pressure comes back into range. You do not need to press anything after refilling; the appliance will simply resume. That auto-clearing behaviour has one awkward side effect worth knowing about. A system sitting right on the threshold can drop below it, stop, recover slightly, and restart, over and over, without anybody seeing a code at all. If your Ferroli is intermittently failing to heat and you can find no fault displayed, marginal pressure is a strong candidate. Check the gauge when the appliance is misbehaving rather than after it has settled.
What causes it
| Cause | What is actually happening | How likely |
|---|---|---|
| Gradual loss over months | Small quantities escape through valve glands and the automatic air vent. Once a year is ordinary and needs nothing but topping up. | Common |
| Radiators bled without topping back up | Bleeding takes water out as well as air. A full round of radiators will move the gauge visibly. | Common |
| Leak on the system | Usually a compression joint under a floor or a weeping valve gland. How quickly the pressure falls is what separates this from ordinary seepage. | Occasional |
| Pressure switch or transducer damaged | Ferroli list this explicitly alongside low pressure. The gauge reads correctly but the appliance still reports a fault, which is the signature of a sensor problem rather than a water problem. | Occasional |
What to try yourself
Read the pressure gauge with the system cold. It should sit between 1.0 and 1.5 bar. If the appliance is cycling on and off, check it while that is happening rather than afterwards.
Find the filling loop below the appliance — usually a braided hose with a lever valve at each end.
Open both valves slowly, watch the gauge, and close them at 1.2 bar. The needle moves quickly through the last part of the range.
Do not exceed 2.5 bar cold. The safety valve will discharge outside and leave you low again once everything cools.Close both valves fully. There is no need to press reset — an F code clears on its own once the reading is back in range, and the appliance should respond to a call for heat within a few seconds.
Note the date. The interval between top-ups is what tells you whether this is maintenance or a leak.
Get a Gas Safe registered engineer to look at your Ferroli F37
Gas Safe Register engineers only. No obligation.
What it costs to fix
Typical repair cost
£0–£450
Time on site
10 minutes
Free if it is a top-up. A pressure switch or transducer is £120 to £200 fitted. A leak trace is £90 to £160 and an expansion vessel £180 to £450.
Typical UK prices including parts and labour, updated August 2026. Your quote may differ.
Parts you may need
We may earn a commission if you buy a part through one of these links. It does not change what you pay, and it does not affect which parts we list.
Expansion vessel (8 litre, sealed system)
EV-8L£35–£85Plumbing merchant
Price checked 5 August 2026
Pressure relief valve, 3 bar
PRV-3B£18–£42Plumbing merchant
Price checked 5 August 2026
What other owners found
Nobody has shared what worked for them on this code yet. If you have had it, you would be the first — and it genuinely helps the next person.
Related Ferroli fault codes
- F.22Get it checkedThe boiler has shut down because there is not enough water in the system. Pressure has dropped below roughly 0.5 bar and it will not fire until you top it up.Related: water pressure
- F.75Get it checkedThe boiler cannot detect a rise in pressure when the pump starts, so it has locked out. Usually a failed pressure sensor or a pump that is not moving water.Related: water pressure
- F1Get it checkedSystem pressure has dropped below the minimum the boiler will run at. Topping it back up to 1.2 bar usually clears it straight away.Related: water pressure
- CE 207Get it checkedSystem water pressure has dropped too low for the boiler to run safely. Topping the system back up to 1.2 bar usually clears it in five minutes.Related: water pressure
- E10Usually simple to fixSystem water pressure has fallen too low for the appliance to fire. Top the system back up to 1.2 bar and it will restart.Related: water pressure
- 108Usually simple to fixThe heating circuit does not contain enough water to run safely. Refill through the filling loop to about 1.2 bar and the code clears.Related: water pressure
Related guides
Sources and how we verified this
We establish the facts from the sources below and then write the explanation ourselves. We do not copy manufacturer wording and we do not host their manuals.
- Manufacturer technical and service documentation