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Worcester Bosch Boiler B7 257 Fault Code

The Worcester fault code B7 257 PCB Q & A or require an engineer for an emergency boiler repair.


The Worcester Boiler Fault Code B7 257 Error Common Q & A

Just below, we have a list of common questions relating to the B7 257 fault code on the Worcester Bosch Boiler.

Worcester Boiler B7 257 Fault Code Error
  • What does the B7 257 fault code mean on my Worcester boiler?
  • What does the PCB do in my Worcester boiler?
  • What are typical signs that a PCB is broken?
  • My boiler keeps locking out and displaying the B7 fault code, what’s the problem?
  • Will resetting the boiler fix the B7 fault code?
  • Can I fit a PCB on a DIY basis?
  • There’s been a burning smell coming from the boiler, what could this be?
  • How does water damage occur in a boiler?
  • What happens if there is a leak in a boiler?
  • Why do heat exchangers leak?
  • Can a leaking heat exchanger be fixed to clear the B7 fault code?
  • Why do heating pumps leak?
  • Will replacing the pump fix the B7 fault code on my Worcester boiler?
  • I don’t think my boiler is leaking, what else could cause a PCB issue?

What does the B7 257 fault code mean on my Worcester boiler?

If your boiler is displaying the B7 fault code with the 257 cause code, it’s an internal error that relates to a printed circuit board (PCB) failure.


What does the PCB do in my Worcester boiler?

The PCB is one of the most important parts of any boiler.

The boiler’s operation is only made possible by a range of parts that send signals to the PCB and receive them in return.

This includes parts such as the:

  • Gas valve
  • NTC thermistors
  • Pump
  • Air pressure switch
  • Fan

As an example, when you turn up your thermostat, the PCB sends a signal to the gas valve to open, providing more gas to the burner.

But let’s say the fan (which takes harmful gases out of your property) stops working – the air pressure switch would tell the PCB, and the boiler would shut off – all due electrical signals.

If the PCB is malfunctioning, it won’t be giving and receiving the correct signals, and your boiler won’t work correctly.

What are typical signs that a PCB is broken?

Any electrical breakdown in a boiler will lead to either no operation, or intermittent operation.

So, you might notice things like:

  • The display panel only works on occasion
  • Radiators get boiling hot, the boiler shuts down until they are cold, and the cycle repeats
  • The boiler turns on and off sporadically, not inline with what’s been set on the timer

Essentially, anything that’s considered out of the norm could be connected to a PCB that’s broken.

My boiler keeps locking out and displaying the B7 fault code, what’s the problem?

There are various sensors that monitor temperatures and pressures in your boiler. When they’re not in tolerance, they feedback this information to the boiler’s PCB, and it will lock out.

However, if the PCB is faulty there’s a good chance it’s giving or receiving the wrong signals.

So, this is going to cause your boiler to lock out randomly.

Will resetting the boiler fix the B7 fault code?

A failure with the boiler’s PCB is permanent. Whilst you may get your boiler running for 30 minutes or so with a reset, it’s not something we’d advise.

Components could be working in conditions that could cause them long-term damage. And long-term damage, means expensive boiler repair bills.

Can I fit a PCB on a DIY basis?

All Gas Safe appliances (boilers, hobs etc) need to be worked on by a qualified professional.

Not only is it dangerous to work on a gas appliance without experience, fitting a part like this could lead to a costly mistake – meaning you complete an expensive repair, that doesn’t fix the problem.

There’s been a burning smell coming from the boiler, what could this be?

As the B7 257 fault code directly relates to a control panel fault, we’d expect this is connections getting burnt out.

This could have been due to old age but on most occasions, it’s water damage that has contributed to these connections failing.

How does water damage occur in a boiler?

Water damage is a widespread problem in boilers. It comes from damaged parts that have started to leak.

There a dozen or more things that can contribute to water damage, but the most common problems are:

  • Cracked heat exchangers
  • Leaking pump seals

What happens if there is a leak in a boiler?

Your boiler is full of important electronic components. When there’s a leak, the water finds itself into these electrical components and causes damage.

Even when the water doesn’t drip directly onto the components, the internal heat of the boiler can create condensation, and it gets in that way instead.

Typically, we find that newer boilers are less prone to these faults, as the electrical components are better sealed than older boilers.

When water damage occurs, it can:

  • Burn out connections
  • Cause a drastic failure with electronic parts it meets

Why do heat exchangers leak?

When old age isn’t a culprit, the problem usually comes from limescale build-up. These mineral deposits come from water. They can settle on components such as the heat exchanger, and when they do they create hot spots.

Unfortunately, where the limescale has settled and the heat exchanger burns hottest, weak spots start to occur.

Over months these hotspots turn into cracks and eventually the heat exchanger starts to leak.

Can a leaking heat exchanger be fixed to clear the B7 fault code?

If it’s the heat exchanger causing the issue, it’s usually unwelcome news.

The heat exchanger can’t be fixed and instead, needs to be replaced. Generally, we’d expect a heat exchanger in a Worcester Bosch boiler to cost somewhere in the region of £500 to replace.

Worst still, this doesn’t fix the issue causing the B7 fault code; it just fixes the leak. You’ll then need to replace the PCB, and that’s likely to be a further £500.

When the heat exchanger and the PCB are faulty in an older boiler, a replacement boiler is usually a much more sensible investment, rather than a repair.

Why do heating pumps leak?

Heating pump leaks usually come from the seals that surround the shaft. These seals can be replaced, assuming the rest of the pump is in good condition.

Typically, we’d replace the whole unit using a quality brand like Grundfos, that will come with a manufacturer’s warranty.

Will replacing the pump fix the B7 fault code on my Worcester boiler?

The same applies here as it does with the heat exchanger. A new pump (which should cost around £250 to replace) will fix the leak, but not the control panel.

So, including the cost of a £500 PCB replacement, the total cost of repair is likely to be £750.

Depending on the age and condition of the rest of your boiler, the wise long-term financial investment is usually with a new boiler.

I don’t think my boiler is leaking, what else could cause a PCB issue?

Old age is just as much a killer as water damage.

You’ll need a boiler engineer to inspect the PCB. Typically, we find that wiring and connections are damaged, and sometimes the circuit board is cracked.

Unfortunately, when there’s a fatal error with a PCB the only real option is a replacement.

If the rest of your boiler’s components are in good condition, it’s worth replacing just the PCB.

However, if your boiler is 5-10 years old, and many of the integral components are showing signs of excessive wear, we’d usually advise replacing the boiler.

Get your boiler engineer to check the state of the:

  • Gas valve
  • Heating pump
  • Heat exchanger
  • Fan
  • Diverter valve

These are the most expensive parts on your boiler.

Other Worcester boiler issues

More more boiler issue regarding the Worcester Bosch the please visit the Worcester Boiler Problems And Cures page.