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8 Reasons Why Your Oil Boiler Isn’t Firing Up For CH/DHW

Welcome to our 5-minute guide to oil boilers that aren’t firing up for central heating and/or hot water.

Below are 8 of the most common oil boiler problems that lead to boilers locking out.

And on that note, resetting your boiler isn’t going to fix the problem. The boiler may work for a minute or two. But, your oil boiler locks out:

  • If it notices a problem whereby continued operation might damage internal components
  • There’s a problem whereby continued operation could lead to the boiler being dangerous.

A long story short, if you have a problem with an oil boiler, get someone that’s qualified to fix or replace it or get a oil boiler service – don’t do it on a DIY basis.

1. Lack Of Fuel

Let’s start with the most obvious. If your boiler doesn’t have enough fuel, it’s not going to fire up.

The Fix

Check your oil tank. Even if there’s a sign of a little oil in the tank, there’s a good chance your fuel supply is starved.

If there’s any debris in the oil tank, a low supply means it’s all collecting at the bottom and that’s going to restrict the fuel supply.

Time for a top up (companies like Boiler Juice offer good deals on heating oil).

2. Incorrect Boiler Pressure

The next most obvious thing to check if your oil boiler is struggling to fire up, is the pressure.

Typically, we’d expect manufacturers to recommend 1.3 bar. However, anything in the 1-3 bar range usually means your boiler will be operational.

An oil boiler with a pressure that’s too high or too low is going to lockout. A reset isn’t going to fix the problem.

The Fix

If your boiler pressure is too high, you need to bleed water from the system. You can do this by locating the drain cock or a radiator bleed valve.

Bleed air and water from the system until the pressure gauge on the boiler drops to 1.3 bar.

If the boiler pressure is too low (below 1.3 bar), you’ll need to add pressure to the system.

Before you do, read this guide to boilers leaking. If your boiler is leaking, you need to get someone to find and fix the problem. Simply topping up water to the system could lead to expensive water damage based repairs in the future.

You’ll be able to do this by opening the valve on the external filling loop.

This is the braided hose that’s located below you boiler’s casing.

3. Condensate Blockage

This is a frequent problem when it’s freezing outside. The condensate vents harmful gases in the form of vapours, out of your property. 

Unfortunately, these condensed gases are prone to freezing.

Generally, if it’s -2 or below outside, there’s a good chance that this is the reason your oil boiler isn’t firing up.

In fact, this problem is so common, that on a recent day where conditions were -6 across the country, we had over 100 questions about boiler lockouts.

Most of these ended up being a frozen condensate pipe that could have been fixed in a matter of minutes and on a DIY basis.

The Fix

They’ll be a small pipe on the exterior of your property. It’s most likely white and 21.5mm in diameter. However, some installers will fit larger condensate pipes in order to reduce the chance of it freezing.

All you need to do is use Luke-warm water (hot water might crack the pipe) and thaw out the pipe.

Once the pipe is thawed, resetting your oil boiler should clear the fault code, and it will fire into life.

As we mentioned, there are precautionary measures that can be taken such as fitting a larger condensate pipe and then protecting it with lagging.

4. Radio Frequency (RF) Pairing

One of the fault codes that aren’t listed frequently online are RF thermostat pairing fault codes.

It’s most likely you’ve got a radio frequency pairing issue if your oil boiler, well, just does what it wants.

That’s going to mean it continues to fire when it shouldn’t, and it won’t fire up for heating and hot water when you ask it to.

If your boiler is working intermittently, it could be something serious like a faulty PCB, but it could be something simple, like the RF pairing.

The Fix

You’ll need to find the owner’s manual for your RF thermostat. That manual is going to show you how to reset to default settings and repair your thermostat.

If you don’t have one, most manufacturers like Salus have manuals online. Just search “Name Of Thermostat”+”Manual”. For instance…”Salus RT500RF Manual”.

5. Radio Frequency Crossover

This is an uncommon boiler problem, but not unheard of.

A thermostat being controlled…by next door!

If you’re on the standard frequency that your RF thermostat offers, and your next door neighbour has the same stat, on the same frequency, guess what happens?

Your house is going to be at the same temperature as theirs. That’s what!

Essentially, one thermostat will control another if it’s in range.

If you’ve noticed your heating switching on randomly after having a new thermostat, there’s a chance it’s next door!

The Fix

Check with your neighbour and see if they have a similar thermostat on the same frequency.

Refer to the thermostat’s owner’s manual which will show you how to switch to a different frequency.

6. Fan Fault

Your oil boiler won’t fire up for central heating or hot water, if the fan isn’t operational.

The fan works with the flue to push the gases from the condensing process out of your property. It’s a safety feature.

The printed circuited board (PCB) needs to signal that the fan is working, before it fires up your boiler.

If there’s a fault with the fan, your oil boiler won’t fire up – it’s as simple as that.

The Fix

If you suspect it’s the fan causing the issue, you’ll need it tested.

We’ve covered boiler fan faults in detail here.

7. Air Pressure Switch Fault

When testing the fan, it’s important to test the air pressure switch too.

The air pressure switch is the device that recognises whether the fan is working or not, based on the air pressure in the boiler and flue.

If it doesn’t recognise the fan working, it will send a signal to the PCB and the PCB will shut the boiler off.

In fact, in your case, there’s a good chance it’s sensing the fan isn’t working from start-up, hence why your oil boiler isn’t firing up at all.

The Fix

Get an accredited engineer to test the air pressure switch and fan in unison.

There’s more details on faulty air pressure switches on boilers here.

8. Printed Circuit Board

The printed circuit board (PCB) on your boiler is the brains. It controls electrical components such as the air pressure switch, fan, gas valve, pump and receives signals from all kind of sensors. 

As soon as it receives a signal that means the boiler isn’t working correctly, it’s going to lock out and display a fault code.

The fault code might be related to the fan, NTC thermistor or even pump.

Problem? If it’s actually the PCB that’s faulty, it’s going to be hard to tell straight away. If it’s faulty, it might not be recognising that the pump’s running, or even that the boiler’s pressure is incorrect.

The Fix

An engineer will be able to research the fault code to see if it relates to PCB faults.

They can then test the PCB on your boiler with a multi-meter. This ensures the PCB is getting power.

We’ve wrote more on faulty boiler PCBs. Unfortunately, the PCB is the most expensive part on the boiler to replace. So, only replace it if:

  • Your oil boiler engineer is 100% confident this is the fault
  • There’s no other major parts that need replacing

Having 2-3 major parts replaced can soon stack up. And if your boiler is old, it makes much more sense to get a quote for a new one.

What’s Next?

Thanks for reading our 5-minute guide to oil boilers that aren’t firing up.

We’ve created a boiler fault finding guide here. Feel free to bookmark it in case you have any problems in the future.

And if you still have a problem with your oil boiler, leave a comment below and we’ll get back to you as soon as possible.




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