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
Then something does not add up, and it is worth knowing why. Despite the wording of the code, Ferroli only list two causes against F37 and both are at the low end — pressure too low, or a damaged pressure sensor. High pressure has its own number on the ranges that publish one: F40, which the Optimax HE 31 C manual defines as pressure too high, above 3 to 5 bar. So a high gauge reading alongside an F37 points at the sensor rather than at the water.
Bring it back to about 1.2 bar cold by bleeding a little water from a radiator into a container, and book an engineer to check the sensor if the code stays. If it climbs steeply again as soon as the heating runs, the expansion vessel needs attention regardless.
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
We do not pass enquiries to a repair firm, so there is no form here. Find a Gas Safe registered engineer through the Gas Safe Register, and ask to see their registration card when they arrive — it is the register, not the van, that tells you they are qualified.
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 September 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 28 September 2026
Pressure relief valve, 3 bar
PRV-3B£18–£42Plumbing merchant
Price checked 28 September 2026
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Related Ferroli fault codes
- A01Get it checkedThe burner failed to light and the appliance has locked out. Ferroli list a blocked siphon as a cause, which is worth checking early.Related: same brand
- A03Get it checkedHigh limit protection has operated. Ferroli point at circulation and at the flow sensor position, and both are worth checking.Related: same brand
- A05Get it checkedThe fan tachometer signal has been missing for an hour or more. The appliance has stopped and needs an engineer.Related: same brand
- A02Stop — call an engineerA flame is being detected while the burner should be off. Switch the appliance off and get a Gas Safe engineer to it.Related: same brand
- F07Get it checkedFlue gas temperature has stayed above 95°C for more than two minutes. Three of these in a day becomes a permanent A04 lockout.Related: same brand
Own a Ferroli boiler? Save it and its codes come first next time.
Related guides
Technical review
Not reviewed by an engineer
No engineer has read this page. Severity follows what the manufacturer publishes, and we would rather tell you that than let a byline imply a sign-off.
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
This page has not been reviewed by an engineer, and we would rather tell you that than imply otherwise. The severity rating follows what the manufacturer publishes: where they say isolate the appliance and call someone, so do we.