Biasi E13 Fault Code: Causes, Fixes & Repair Costs
What does the Biasi E13 fault code mean?
The Biasi E13 fault code — also displayed as ER 13 on older Biasi models such as the Riva Plus and Garda, and as E13 on newer models including the Inovia, Rinnova, and Rinnova Adaptive — indicates that the boiler has detected an excessive temperature difference between the flow (flow/mandata) pipe and the return (ritorno) pipe of more than 40 Kelvin (40°C). In practical terms, this means water is leaving the boiler very hot but returning far too cool, which almost always points to a circulation problem within the heating system. The boiler locks out to protect the heat exchanger from overheating. On some Biasi Inovia firmware variants, E13 is described as relating to a faulty pump or primary temperature exceeding 105°C — which is consistent with the same root cause: water is not flowing around the system fast enough.
General guidance only — not a substitute for professional advice, and not certified by a Gas Safe engineer. Always have your specific appliance assessed by a qualified professional. Any gas work must be carried out by a Gas Safe registered engineer. If you smell gas or suspect carbon monoxide, leave the property and call the National Gas Emergency line on 0800 111 999.
Common causes
- Circulation pump failure or seizure Common
The pump is responsible for pushing heated water around the system. If it has seized, is running too slowly, or has failed entirely, water stagnates near the heat exchanger, causing the flow temperature to spike while the return stays cool. A seized pump is the single most common cause of an E13 on Biasi boilers and should be the first thing an engineer checks.
- Sludge or scale blocking the heat exchanger Common
Over time, black iron oxide sludge (magnetite) and limescale can accumulate inside the primary heat exchanger, severely restricting water flow through it. Even if the pump is working, water cannot pass through quickly enough, causing the same excessive temperature differential. This is particularly common in older systems or those without a magnetic filter fitted.
- Low system pressure Common
If the system pressure has dropped below around 1 bar, there is less water available to absorb and carry heat away from the exchanger. This reduces effective flow rate and amplifies the temperature difference between flow and return. Check the pressure gauge on the boiler — it should read between 1 and 1.5 bar when the system is cold.
- Air locked in the system Sometimes
Trapped air in radiators or pipework reduces the volume of water circulating effectively, creating hot spots and causing the boiler to see an inflated Delta T. Bleeding radiators removes air pockets and can restore normal circulation.
- Too many radiator valves or TRVs closed simultaneously Sometimes
If thermostatic radiator valves (TRVs) throughout the home are all closed or turned down to their lowest setting at the same time, there is insufficient flow path for water to circulate. The boiler then struggles to dissipate heat, causing the flow-return differential to rise sharply. At least one radiator (ideally the one closest to the boiler) should be left fully open.
- Faulty flow or return NTC temperature sensor Sometimes
If one of the NTC temperature probes — either on the flow outlet or the return inlet of the primary heat exchanger — is giving inaccurate resistance readings, the PCB may calculate a false Delta T and trigger E13 even when actual circulation is fine. A borderline or intermittently failing probe is worth testing before replacing the pump. Note that the related code E12 specifically flags a return NTC failure; E13 can appear when a probe fault is subtler.
How to fix it
- Reset the boiler once DIY safe
Press and hold the reset button for 3–5 seconds as described in your model's user manual (the exact button location varies between Rinnova, Inovia, and older ER-series models). If the fault clears and does not return, monitor the boiler over the next hour. Do not reset more than two or three times — repeated resets without fixing the underlying problem simply delay the right repair and can mask a worsening fault.
- Check the system pressure DIY safe
Look at the pressure gauge on the boiler fascia. It should read between 1.0 and 1.5 bar when the system is cold. If it is below 1 bar, locate the filling loop (a flexible braided hose or built-in valve beneath the boiler), slowly open both valves until the gauge reaches approximately 1.2 bar, then close the valves firmly. Reset the boiler and observe. If pressure drops again within days, there is likely a leak somewhere — call an engineer.
- Bleed your radiators DIY safe
If some radiators feel cold at the top or gurgling sounds are present, air may be trapped in the system. Use a radiator bleed key to open the bleed valve on each radiator (starting with the furthest from the boiler and working back) until water — not air — flows out steadily. Retighten the valve, then re-check system pressure as bleeding can cause a small pressure drop.
- Check thermostatic radiator valve (TRV) settings DIY safe
Walk around the home and ensure that not all radiators are turned down to their lowest setting simultaneously. If every TRV is closed, water has nowhere to flow and the boiler will overheat rapidly. Leave at least one radiator — ideally the hallway radiator or the one nearest the boiler — fully open at all times to maintain a minimum flow path through the system.
- Have the circulation pump inspected and tested Gas Safe engineer
A Gas Safe engineer will check whether the pump is running at the correct speed, producing adequate flow, or has seized. A seized pump can sometimes be freed without replacement, but a pump that has failed electrically or mechanically will need to be replaced. This is an internal boiler component and must not be touched by anyone who is not Gas Safe registered.
- Have the NTC flow and return temperature sensors tested Gas Safe engineer
An engineer will measure the resistance of both the flow and return NTC probes at a known water temperature and compare the readings against the manufacturer's specification. A probe giving out-of-range readings will be replaced. Faulty probes cause the PCB to misread the Delta T and can trigger E13 spuriously.
- Arrange a powerflush if sludge is suspected Gas Safe engineer
If the engineer finds that the heat exchanger or pipework is heavily sludged, a powerflush is the most effective remedy. This involves connecting specialist equipment to force clean water and descaling chemicals at high velocity through the entire system, dislodging and flushing out magnetite and scale. A magnetic system filter should then be fitted to prevent recurrence. This work must be carried out by a suitably qualified heating engineer.
- Call a Gas Safe registered engineer if the fault persists or you cannot identify the cause Gas Safe engineer
If the boiler continues to display E13 after checking pressure, bleeding radiators, and adjusting TRVs, the fault requires professional diagnosis. An engineer can systematically test the pump, both NTC sensors, the heat exchanger flow rate, and the PCB to identify the exact cause. You can verify any engineer's Gas Safe registration at gassaferegister.co.uk before they start work.
Parts you may need
- Circulation pump (compatible replacement) · from £120
- Flow NTC temperature sensor · from £25
- Return NTC temperature sensor · from £25
- Magnetic system filter (e.g. Fernox TF1 or Adey MagnaClean) · from £55
- PCB (printed circuit board) · from £180
The exact spare depends on your boiler's GC number (on the data badge). Check this against the part before buying.
Typical repair cost
Expect to pay roughly £140–£450, depending on the underlying cause.
Frequently asked questions
What is the difference between E13 and ER 13 on a Biasi boiler?
They are the same fault expressed differently depending on the model generation. Older Biasi boilers such as the Riva Plus and Garda use the ER prefix (ER 13), while newer models including the Inovia, Rinnova, and Rinnova Adaptive display the fault simply as E13. The meaning is identical in both cases: the temperature difference between the flow and return pipes has exceeded 40°C, indicating a circulation problem.
Can I fix Biasi E13 myself?
There are a few safe checks a homeowner can do: top up system pressure to around 1.2 bar using the filling loop, bleed any air from radiators, check that radiator valves are not all closed, and try a single reset. However, if these steps do not clear the fault, the cause is almost certainly mechanical — a failing pump, blocked heat exchanger, or faulty sensor — all of which require a Gas Safe registered engineer. Do not attempt to open the boiler casing or touch internal components.
How much does it cost to fix Biasi E13?
The most common repairs fall in the range of £140–£450 including parts and labour. A straightforward pump repair or sensor replacement tends to sit at the lower end, while a full pump replacement typically costs £280–£420 all-in. A powerflush, if significant sludge is found, usually adds £350–£600 on top. In the uncommon situation where a PCB is the root cause, expect £250–£450 for the part alone plus labour. If a quote approaches or exceeds £500, it is worth getting a new boiler comparison, as Biasi themselves suggest models carry a 5–7 year warranty — check whether yours is still covered before paying for a major repair.
Why does my Biasi boiler keep showing E13 after I reset it?
A reset clears the lockout but does nothing to fix the underlying fault. If E13 keeps returning — especially within minutes of a reset — the circulation problem is still present. The most likely culprits are a pump that is struggling or has seized, a heat exchanger heavily restricted by sludge, or a sensor giving inaccurate readings. Repeated resets in this situation simply delay the repair and can put additional thermal stress on the heat exchanger. Book a Gas Safe engineer to diagnose and resolve the root cause.