Remeha H.00.17 Fault Code: Causes, Fixes & Repair Costs
What does the Remeha H.00.17 fault code mean?
On Remeha boilers running the e-Smart control platform, fault codes are structured in three parts. The letter 'H' means this is a blocking fault — a temporary safety shutdown that may clear once the underlying condition is resolved, as opposed to an 'E' code which represents a permanent lockout. The '00' group covers primary safety functions, particularly flow temperature and overheat protection. The sub-code '17' indicates the boiler's flow temperature has climbed to an unsafe level and the safety system has intervened to shut the appliance down before damage can occur. In plain terms: the boiler's water has got too hot, and it has cut out to protect itself and your home. The root cause is typically a flow or circulation problem — not enough water moving through the system fast enough to carry heat away from the heat exchanger. This code appears on models such as the Tzerra Ace, Quinta Ace, and Gas 320/620 Ace series. A closely related blocking fault, H.01.05, behaves similarly and has been reported by users as the boiler firing too aggressively, climbing above 90°C, and then immediately tripping — H.00.17 follows the same logic but flags the condition via the primary safety temperature group.
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
- Poor water circulation due to pump failure or airlock Common
If the circulating pump is struggling, seized, or partially blocked by sludge, water cannot move around the system quickly enough. Heat builds up in the heat exchanger, and the flow temperature spikes. An airlock in the pipework produces the same effect — even a healthy pump cannot push water past a trapped bubble. This is the single most common trigger for this type of overheating fault on Remeha e-Smart boilers.
- Low system water pressure Common
If the system pressure has dropped below around 1 bar — perhaps after bleeding radiators or due to a small, slow leak — there is less water volume in the circuit to absorb and carry away heat. The reduced thermal mass makes it much easier for the flow temperature to overshoot its safe limit and trigger H.00.17.
- Sludge or limescale restricting flow Common
Over time, heating systems accumulate black iron oxide sludge and, in hard-water areas, limescale. Both narrow the internal bore of pipework, radiators, and the heat exchanger itself. Restricted flow has the same effect as a failing pump — insufficient water movement, rising flow temperature, and a safety shutdown.
- Faulty or degraded flow temperature sensor Sometimes
The e-Smart controller reads the flow temperature from a thermistor sensor. If that sensor has drifted out of calibration, has a loose electrical connection, or has suffered water ingress, it may report a temperature that is higher than reality — causing the boiler to shut down even when actual conditions are acceptable. Conversely, a sensor that under-reads could allow genuine overheating to develop undetected before a separate safety device intervenes.
- Scaled or partially blocked heat exchanger Sometimes
In hard-water areas especially, limescale deposits build up on the internal surfaces of the heat exchanger. The scale acts as an insulator, trapping heat in the water rather than allowing it to transfer efficiently. The flow temperature climbs rapidly under even moderate firing rates, and the boiler shuts down on overtemperature.
- Faulty PCB or wiring fault Rare
If the control board itself is misreading sensor signals, or if wiring to the pump or temperature sensors is damaged or corroded, the boiler may behave as though it is overheating when the hydraulic side is actually fine. This is a less common cause and is usually only confirmed after other causes have been ruled out.
How to fix it
- Check the system pressure gauge DIY safe
Look at the pressure gauge on the front of the boiler. It should read between 1.0 and 1.5 bar when the system is cold. If it is below 1 bar, top it up using the filling loop — usually a braided flexible hose with one or two valves located beneath the boiler. Open the valve(s) slowly, watch the gauge rise to around 1.2 bar, then close the valve(s) fully. If the system loses pressure again within a few days, there is a leak somewhere that needs professional attention.
- Bleed your radiators to release any trapped air DIY safe
Turn the heating off and allow the system to cool. Using a radiator bleed key, open the bleed valve at the top corner of each radiator in turn — start upstairs and work downwards. Hold a cloth underneath to catch drips. When water (rather than air) flows steadily from the valve, close it. Check the boiler pressure again afterwards and top up if it has dropped below 1 bar.
- Reset the boiler — once or twice only DIY safe
Press and hold the reset button on the boiler's front panel as described in your user manual (typically around 3 seconds until the display responds). Allow the boiler a full 60 seconds to attempt a restart before judging whether it has cleared. If it trips to H.00.17 again immediately, do not keep resetting — repeated resets without fixing the root cause can mask a worsening problem. Two attempts is the sensible maximum before calling an engineer.
- Check the flue terminal outside DIY safe
Go outside and look at where the flue exits the building. Make sure it is not blocked by debris, bird nesting material, or ice. A restricted flue can affect combustion quality and indirectly contribute to overheating conditions. Do not touch or modify the flue terminal — just visually check it is clear.
- Have a Gas Safe engineer test the circulation pump Gas Safe engineer
An engineer will check the pump is receiving power, running at the correct speed, and moving adequate water flow. They can manually turn the pump spindle to check for seizure and inspect the wiring connections. A faulty pump is one of the most common causes of this fault and is straightforward to replace once confirmed.
- Have a Gas Safe engineer inspect and test the flow temperature sensor Gas Safe engineer
Using a multimeter, an engineer can measure the resistance of the thermistor at a known water temperature and compare it against the manufacturer's specification table. A sensor reading outside the expected range will be replaced. Wiring integrity and connector condition are checked at the same time.
- Have a Gas Safe engineer assess the system for sludge and scale Gas Safe engineer
If the pump and sensors test as serviceable, the engineer will assess whether restricted circulation from sludge or limescale is the culprit — for example by checking the temperature differential between flow and return pipes, or by inspecting the magnetic filter (if fitted). A power flush may be recommended to clear debris and restore proper flow throughout the system.
- Have a Gas Safe engineer inspect the heat exchanger Gas Safe engineer
In hard-water areas or older systems, the heat exchanger may have significant limescale deposits. An engineer can assess the degree of scaling and advise whether a chemical descale, a replacement heat exchanger, or a whole-system flush is the most cost-effective solution.
- Have a Gas Safe engineer check the PCB and wiring loom Gas Safe engineer
If all hydraulic and sensor checks pass, the fault may lie with the control board itself misinterpreting sensor data, or with damaged wiring. PCB diagnosis and replacement must be carried out by a qualified engineer. This is typically the last avenue explored because it is the most expensive component and rarely the primary cause.
- Call a Gas Safe registered engineer if the fault persists Gas Safe engineer
If the steps you can do yourself have not resolved H.00.17, stop resetting the boiler and arrange for a Gas Safe registered engineer to diagnose it properly. You can verify any engineer's registration at gassaferegister.co.uk. Continuing to run a boiler that is repeatedly overheating without identifying the cause can cause serious damage to the heat exchanger or other components.
Parts you may need
- Flow temperature sensor (thermistor) · from £22
- Circulation pump (e-Smart compatible) · from £95
- Magnetic system filter (e.g. Fernox TF1 or equivalent) · from £55
- PCB / control board · from £280
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–£380, depending on the underlying cause.
Frequently asked questions
Can I reset a Remeha H.00.17 fault myself?
Yes, a single reset is a reasonable first step — but only after you have checked system pressure and bled any trapped air. Press the reset button as described in your user manual and wait to see whether the boiler stays running. If it trips back to H.00.17 within minutes, do not keep resetting it. Two attempts is a sensible limit. Persistent overheating faults need a Gas Safe engineer to find and fix the root cause rather than repeatedly clearing the symptom.
How much does it typically cost to fix a Remeha H.00.17 fault in the UK?
For the most common causes — a circulation pump replacement or a flow sensor swap — most homeowners pay somewhere between £120 and £380 all in, including parts and labour. A pump replacement with labour tends to sit around £200–£300, while a sensor is a more modest repair once you add the call-out charge. If the system needs a full power flush to clear sludge, budget £300–£500 depending on the number of radiators and your location. Rare big-ticket repairs such as a new heat exchanger (£400–£600) or PCB (£250–£450) sit outside the typical range — your engineer should be able to narrow down the cause before committing to those.
What is the difference between an 'H' fault and an 'E' fault on a Remeha boiler?
On Remeha's e-Smart platform, 'H' codes are blocking faults — temporary safety shutdowns where the boiler may be able to restart once the fault condition clears or is reset. 'E' codes are permanent lockouts that require a manual reset and usually indicate a more serious or confirmed fault that the boiler will not attempt to recover from automatically. H.00.17 is a blocking fault, which is why a careful reset is worth trying, but it should not be treated as a minor inconvenience if it keeps returning.
Could low boiler pressure be causing my Remeha H.00.17 fault?
Yes, this is one of the more straightforward causes. If system pressure has dropped below 1 bar, there is less water in the circuit to absorb the heat the burner produces. The flow temperature rises faster and more steeply, eventually triggering the overheating shutdown. Top the pressure up to around 1.2 bar using the filling loop and attempt a reset. If this resolves it and the pressure stays stable, you may have simply needed a top-up. If the pressure keeps dropping, there is a leak in the system — possibly from a radiator valve, a pipe joint, or the boiler itself — and an engineer should investigate.