224 V is the Worcester Bosch 8000 series equivalent of the E9 overheat fault — and it’s the one Edinburgh homeowners with a newer Greenstar 8000 are most likely to encounter when their boiler locks out due to a temperature issue.
The code means the safety temperature sensor has detected temperatures above the safe threshold — either because the boiler is genuinely overheating or because a sensor or component is misfiring.
Either way, the boiler shuts down to protect itself, and it needs investigating before you reset it.
What Does 224 Mean on a Worcester Bosch 8000?
On the Greenstar 8000, 224 V signals that the safety temperature limiter has tripped due to the flow temperature hitting or exceeding the cut-off point — typically around 105°C in the central heating circuit, or 130°C at the safety sensor. It’s a locking fault, so the boiler won’t restart automatically.
Worcester Bosch error code guidance confirms that the first step after an EA 224 lockout is to check water pressure and attempt a single reset after the system cools — but if it returns, professional diagnosis is needed.
What Causes 224 on a Worcester Boiler?
Is a Pump Problem Behind 224?
As with E9 on older models, a failing or poorly circulating pump is the most common cause of 224. When the pump can’t move water around the system fast enough, heat builds up in the heat exchanger faster than it can be dissipated — temperatures rise, the limiter trips, and 224 appears.
If your Greenstar 8000 has been making any unusual sounds or if radiators have been slow to reach temperature recently, the pump is the first place an engineer will look.
Could Low Water Pressure Be Causing 224?
Yes, and this is worth checking yourself before calling anyone. Low pressure reduces the volume of water circulating through the system, which can contribute directly to heat build-up and an 224 lockout.
Worcester Bosch specifically flag this in their own troubleshooting guidance for the 224 fault. Check the display or pressure gauge — on the 8000 series, low pressure also triggers fault code 1017 W independently. Top up to 1–1.5 bar if needed, let the system cool, then reset once.
Is the Safety Temperature Sensor Faulty?
The 224 fault doesn’t always mean the boiler is actually overheating — a faulty safety temperature sensor can report false high readings that the control unit takes at face value and responds to by shutting the boiler down.
This is a common cause of 224 faults that return almost immediately after reset even when pressure is fine and the pump appears to be running. Sensor replacement is a relatively straightforward repair for an engineer and considerably cheaper than a heat exchanger or pump job.
Could a Blocked Condensate Pipe Trigger 224?
In Scottish winters, yes — a frozen or blocked condensate pipe can disrupt the boiler’s operation enough to cause abnormal temperature readings and a 224 lockout.
Check the external white plastic pipe for ice before calling an engineer in cold weather. Thaw with warm water and reset once to see if the fault clears.
What About a Faulty Diverter Valve or Blockage?
On combi boiler variants of the Greenstar 8000, a sticking diverter valve can restrict water flow through the heat exchanger — reducing circulation efficiency and causing temperatures to climb toward the 224 trip point. An engineer will test valve operation and check for any partial blockages in the primary circuit during diagnosis.
What Should You Do When 224 Appears?
Let the boiler cool down for 10–15 minutes first — resetting a hot boiler immediately after a 224 lockout sometimes clears the code only for it to return seconds later, which doesn’t tell you anything useful.
While it cools, check the pressure gauge and top up if below 1 bar. Check the condensate pipe in cold weather.
Once cooled, attempt a single reset. If the boiler fires and runs normally, monitor it carefully over the next 24 hours. If 224 reappears — either immediately or within a day — stop resetting and call a Gas Safe engineer.
Repeated resets on a genuine overheat fault risk damaging the heat exchanger and other components that would otherwise be fine.
How Much Does It Cost to Fix 224?
| Cause | Typical Repair Cost |
|---|---|
| Low pressure (top-up) | £0 |
| Frozen condensate (DIY) | £0 |
| Safety temperature sensor replacement | £150–£300 |
| Diverter valve replacement | £200–£350 |
| Pump replacement | £200–£400 |
| Heat exchanger descale or replacement | £300–£600 |
| PCB replacement | £300–£500+ |
Does Annual Servicing Prevent 224?
For pump-related and sludge-related causes — yes, in most cases. A proper annual service on a Greenstar 8000 includes checking pump operation, cleaning the magnetic filter, and inspecting the heat exchanger for early signs of scaling. Our service costs £110 + VAT and is the most cost-effective way to keep 224 and other overheat faults at bay.
Book a boiler service or arrange a repair with our Edinburgh engineers today.
Need 224 Fixed in Edinburgh?
Our Gas Safe registered engineers work on the full Worcester Bosch Greenstar 8000 range across Edinburgh every day. Call 0131 510 8500 or contact us online and we’ll get someone out to you.
If your 8000 is faulting regularly or a major component repair is on the cards, get a free quote for a replacement at the same time — we’ll give you an honest view on whether repair or replacement makes more financial sense for your specific boiler.
