Remeha E1 Fault Code: Flow Temperature Exceeds Maximum Limit
The E1 code appears when your Remeha boiler detects that the water temperature leaving the heat exchanger (the flow temperature) has climbed above the maximum permitted threshold. As a safety response, the boiler shuts itself down to prevent damage or a dangerous overheat situation. In most cases the boiler will attempt to restart but will lock out again quickly if the underlying cause is not addressed. This fault is most commonly seen on the Remeha Avanta range and is nearly always linked to a problem with water circulation — either not enough water in the system, air trapped in the circuit, or something physically preventing water from moving freely around the heating loop.
General guidance only — not a substitute for professional advice. 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.
What does the Remeha E1 fault code mean?
The E1 code appears when your Remeha boiler detects that the water temperature leaving the heat exchanger (the flow temperature) has climbed above the maximum permitted threshold. As a safety response, the boiler shuts itself down to prevent damage or a dangerous overheat situation. In most cases the boiler will attempt to restart but will lock out again quickly if the underlying cause is not addressed. This fault is most commonly seen on the Remeha Avanta range and is nearly always linked to a problem with water circulation — either not enough water in the system, air trapped in the circuit, or something physically preventing water from moving freely around the heating loop.
Common causes
- Low system pressure Common
If the water pressure in your central heating system has dropped below around 1 bar, there is simply not enough water circulating to carry heat away from the heat exchanger efficiently. Temperatures rise quickly and the boiler's safety limiter triggers the E1 shutdown. This is the single most common cause of this fault and is worth checking first.
- Trapped air or airlock in the system Common
Air pockets in the radiators or pipework prevent water from circulating properly. Even with adequate pressure on the gauge, an airlock can starve part of the circuit of flow, causing localised overheating that triggers the E1 code. Radiators that are cold at the top but warm at the bottom are a tell-tale sign.
- Circulation pump failure or seizure Sometimes
The pump is responsible for pushing heated water around the system. If it has seized, is running too slowly due to wear, or has become clogged with sludge, water stalls in the heat exchanger and temperatures spike rapidly. A pump that hums but does not move water is a classic symptom.
- Sludge or scale blockage in the system Sometimes
Over time, magnetite sludge and limescale can build up inside pipework, radiators, and the boiler's internal waterways. This restricts flow in the same way a kinked hose would, causing hot spots and triggering the overheat protection. Systems without an in-line magnetic filter are particularly vulnerable.
- Faulty flow temperature sensor (NTC sensor) Rare
The sensor that measures the outgoing water temperature can develop a fault and report an artificially high reading. The boiler reacts as though overheating is occurring even when the actual water temperature is perfectly normal. This is less common than the hydraulic causes above but should be considered when all other checks come back clear.
How to fix it
- Check the pressure gauge on the boiler DIY safe
Look at the pressure gauge on the front of your Remeha boiler. The needle should sit between 1.0 and 1.5 bar when the system is cold. If it is below 1 bar, this is almost certainly contributing to the E1 fault and you should top up the system using the filling loop before doing anything else.
- Top up system pressure using the filling loop if needed DIY safe
Locate the filling loop — usually a flexible braided hose with one or two valves beneath the boiler. Slowly open the valve(s) and watch the pressure gauge rise. Stop once it reaches approximately 1.2 bar. Close the valve(s) fully and check the gauge holds steady. Never overfill beyond 1.5 bar. If the system loses pressure again within a day or two, there is a leak somewhere that an engineer needs to locate.
- Bleed the radiators to release trapped air DIY safe
Starting with the radiator furthest from the boiler and working back towards it, use a bleed key to open the bleed valve (usually a square nipple at the top corner of each radiator) a quarter turn anti-clockwise. Hold a cloth beneath it. When a steady stream of water appears with no spluttering air, close the valve. Check the boiler pressure again afterwards and top up to 1.2 bar if it has dropped. Do not bleed radiators with the boiler firing — turn it off and let it cool first.
- Reset the boiler DIY safe
Once pressure is correct and radiators have been bled, press the reset button on the boiler's front panel and allow it to restart fully. If it fires up and runs normally, monitor it over the next hour. If it locks out again with E1, do not keep resetting it — repeated lockouts indicate an underlying fault that requires professional diagnosis.
- Call a Gas Safe registered engineer for further investigation Gas Safe engineer
If the E1 fault returns after the checks above, a qualified engineer needs to take over. They will assess the circulation pump for correct operation and flow rate, check the system for sludge accumulation (and recommend a power flush if needed), test the flow temperature NTC sensor for accurate readings, and inspect internal components such as the heat exchanger and PCB. Do not attempt to access or test any of these components yourself.
Parts you may need
- NTC flow temperature sensor · from £25
- Central heating circulation pump (e.g. Grundfos UPS2 15-50) · from £85
- Magnetic system filter (e.g. Magnaclean Pro2) · from £60
- Pressure relief valve · from £20
- Filling loop assembly · from £15
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 £120–£400, depending on the underlying cause.
Frequently asked questions
Can I fix the Remeha E1 fault myself?
The initial checks — verifying system pressure, topping up via the filling loop, bleeding radiators, and performing a single reset — are safe for a homeowner to carry out. However, if the boiler continues to display E1 after these steps, the fault moves into territory that requires a Gas Safe registered engineer. Investigating the pump, sensors, heat exchanger, or PCB is not safe or legal for an unqualified person to attempt.
How much will it cost to repair a Remeha E1 fault?
If the fix is simply repressurising and bleeding, the cost is effectively nothing if you do it yourself, or a standard call-out fee of around £80–£100 if you prefer an engineer to do it. More involved repairs — such as replacing a circulation pump (typically £185–£300 including parts and labour) or carrying out a power flush to clear sludge (£350–£500) — sit at the higher end. A flow temperature sensor replacement usually falls in the £80–£150 range. In rare cases where the PCB or heat exchanger is at fault, costs can exceed £500, but this is not typical for an E1 code.
Why does my Remeha boiler keep coming back with E1 even after I reset it?
A boiler that repeatedly locks out with E1 is telling you that the root cause has not been resolved. Each time it fires up, the flow temperature climbs too fast — usually because water is not moving freely enough around the system. The most likely culprits are a failing circulation pump, a significant sludge blockage, or a sensor fault. Continuing to reset the boiler without addressing the cause can stress internal components further, so arrange for a Gas Safe engineer to carry out a proper diagnosis.
Could low boiler pressure really cause an E1 overheat fault?
Yes — it is one of the most common triggers. When there is insufficient water in the circuit, the small volume of water that is present heats up very rapidly. The heat exchanger cannot transfer heat quickly enough, the flow temperature overshoots the safety limit, and E1 is triggered. Checking and correcting the pressure to 1.0–1.5 bar is always the first and simplest thing to try.