The 7 Most Common Viessmann Boiler Problems [and The Fixes]

Welcome to our 3-minute guide to Viessmann boiler problems, their symptoms, fault codes, and fixes.

Not all boiler problems are terminal, so hopefully, this troubleshooting guide will help you make sense of the fault and get your boiler fixed ASAP.

Before we start — we’ll always advise getting help from a Gas Safe engineer if you need to fix a problem with your Viessmann gas boiler.

No Time to Read? Viessmann Boiler Problems Summary

If you prefer to jump straight to your fault instead of reading the entire guide to Viessmann boiler problems, go ahead and find the link to your issue below:

1. Viessmann boiler no hot water
2. Radiators not heating up fully
3. Boiler burner blocked — Viessmann fault codes A3, B0, F1, F-E1, F-E2
4. Burner lockout — Viessmann F2, E1, E7, E8, E9, EA, EB, EC fault codes
5. Faulty boiler burner — F-B7, F-F4, F-F2, F-F7, F-F8, F-F9, F3, F9, F10, F13, and F4 fault on Viessmann boiler
6. Noisy heating pump — A8 fault code
7. Viessmann boiler won’t fire up — F5 fault code

7 Common Viessmann Boiler Problems

Below, we’ve listed the most common Viessmann boiler problems. Keep in mind that not all of these issues have a corresponding fault code, so we’ve listed fault codes only where applicable.

#1 – Viessmann Boiler No Hot Water, But Heating Works

If your central heating system is up and running but there’s no hot water, there are a few potential culprits.
This is one of the most common Viessmann boiler problems, particularly with the Vitodens 100 and Vitodens 200 models.

Although there are various explanations, there’s a good chance that your boiler engineer will diagnose a faulty diverter valve.

Diverter valves switch between hot water and heating systems. If a diverter valve wasn’t fitted, your radiators would heat up every time you call the boiler for hot water.

Now if your diverter valve is faulty or stuck (on the heating side), this would explain why the heating works, but the boiler is not heating water in the taps.

The Fix

If your Viessmann boiler is particularly old, there’s a good chance your diverter valve can’t be repaired. On average, a Viessmann boiler diverter valve costs around £350 to be replaced (depending on the boiler model).

If you’ve boiler is over 10 years old, other parts could be degrading, too. Have your Gas Safe engineer check over the most expensive parts in your boiler (burner, heat exchanger, pump and fan). A good boiler care plan should cover the replacement costs of these parts if they look like they’re about to fail.

However, if you haven’t got boiler cover, your boiler is out of warranty, and the internal components are failing, it’s worth considering a boiler replacement. You can get an online price for a new one in less than two minutes by filling Heatable’s 90-second form.

#2 – Radiators Not Heating Up Fully

This is another one of those Viessmann boiler problems that could have 3 possible explanations; let’s go through them below.

Radiators Only Half Heating Up

This is the only symptom that signifies a boiler fault.

It’s typically a sign of a temperature control or a water circulation problem.

Hot at the Top, but Cold at The Bottom

This problem isn’t boiler related — central heating sludge is the real culprit here.

Read why your radiators are only hot at the top here.

Cold at the Top, but Hot at the Bottom

Radiators that are cold at the top usually signify an air lock. You’ll need to bleed the radiators to remove this air lock.

All you need is a radiator bleed key (like this one), which you can use to slowly open the valve until the air stops hissing and water starts dripping out.

The Fix

Assuming your radiators are just half-heated with even temperature throughout, you’ll need to check for:

• Heating pump faults
• Flow and return temperature sensors (NTC thermistors)

A Gas Safe engineer will be able to check the heating pump for leaks, a seized motor, and whether the flow setting is correct. They’ll then be able to use a multi-meter to check the NTC thermistors electrical current and resistance. If they are faulty, they need to be replaced.

If the NTC thermistors show no sign of damage, there’s a chance there’s limescale build-up around them.

Limescale creates uneven temperature readings, so the NTC thermistors can’t monitor it correctly. Because of this, the signals they send back to the circuit board are intermittent.

Usually, the limescale settles near the thermistor. And, the thermistor thinks the overall water temperature is much higher than it is. This causes the boiler to shut off prematurely.

ALSO READ: Where are Viessmann boilers made?

#3 – Boiler Burner Blocked

Possible fault codes: A3, B0, F1, F-E1, F-E2

Next on our list of Viessmann boiler problems is a blocked burner.

A burner fault on your Viessmann boiler may be hard to diagnose without taking the boiler apart. And that’s a job for a Gas Safe engineer. The most common Viessmann fault code displayed for a burner blockage is the F1 error, which you’ll see this on your display panel. However, some models will display A3, B0, F1, F-E1, and F-E2.

Usually, these fault codes actually relate to a flue gas sensor problem.

The Fix

The most common fix here is the check the flue sensor. Usually, this part will be faulty and in need of replacement.

If you’d prefer to invest that cash into a new and reliable boiler, you can get prices from Heatable here. Not only are they competitive with their costs, but they offer 10-year warranties and flexible financing.

#4 – Viessmann Boiler Burner Lockout  

Possible fault codes: F2, E1, E7, E8, E9, EA, EB, EC

A burner lockout is one of the few Viessmann boiler problems that won’t give a clear indication of what’s wrong.

The most common fault code that’s displayed is the Viessmann F2. That said, older boilers (such as the Vitocrossal 200) may display errors such as the E1, E7, E8, E9, EA, EB, EC and F2 error codes.

Typically, this code means that there’s a blockage somewhere. And the easiest place to start troubleshooting is the central heating pump in your boiler.

The Fix

This circulation fault causes the burner to lockout, but it’s not usually the burner that’s at fault.

When the burner heats water, it needs the pump to circulate it; if it doesn’t the boiler can quickly overheat.

An air lock is a common pump problem that can cause this; we’ve written about boiler pump airlocks here.

#5 – Faulty Burner 

Possible fault codes: F-B7, F-F4, F-F2, F-F7, F-F8, F-F9, F4, F3, F9, F10, F13

Now, if you have a faulty burner (as opposed to one that can’t operate safely because of other faulty parts), there are specific fault codes that indicate this condition.

For example, the Viessmann Vitocrossal 200 may display fault codes such as F-B7, F-F4, F-F2, F-F7, F-F8 and F-F9. Meanwhile, the Viessmann F4 fault, as well as error codes F3, F10, and F14 are more likely on a Vitodens 200.

The actual reason the boiler is locking out is that there’s no flame present, no signal of a flame, or the flame is weak.

The Fix

An engineer will first need to check that the flame sensor is working. On some occasions, it simply needs cleaning.

Next, they’ll need to check the burner itself. Hopefully, it’s clogged with debris but not broken.

Finally, if the burner and flame sensor appear to be working, the engineer will need to test the PCB (Printed Circuit Board), which communicates with the sensor and burner. If it’s broken, neither will work.

If you’re looking at expensive repair bills for a boiler that’s out of warranty, consider getting prices for fitting a new boiler instead. You can get a cheap boiler installed via Heatable — check out their prices on your screen here.

#6 – Noisy Heating Pump, Or Cold Return Pipes 

Possible fault codes: A8

If you’ve got a noisy heating pump, there’s a good chance you also have cold return pipes and your boiler will be showing a A8 fault code.

Typically, this means the heating pump is blocked with dirt or has an airlock. Luckily, both problems are quite easy to fix.

The boiler monitors water circulation. When it sees the minimum flow rate has not been achieved, it will lock out, which is what’s happened here.

The Fix

Your Gas Safe engineer will have to clean the pump and inspect it for damage.

Assuming the pump is in working condition, the engineer may need to alter the flow settings to give the heating system a boost and meet the minimum flow rate the boiler requires.

#7 – Viessmann Boiler Won’t Fire Up

Possible fault codes: F5

If your Viessmann boiler problem relates to a unit that won’t ignite, there are a few potential causes.

Viessmann states this is a fault with the burner. If this part is clogged with debris, that’s enough to cause the fault and an F5 fault code.

However, it’s more likely there’s an issue related to the air pressure sensor (not to be confused with the boiler pressure gauge).

The Fix

First, the heating engineer will need to clean and inspect the burner.

Next, they’ll have to test the air pressure sensor; we’ve created a quick sensor fault finding guide here. This sensor tells the boiler that air pressure is within safe operating range. If there’s a fault with the sensor, wiring, or the circuit board it communicates with, the boiler won’t ignite.

To rectify the issue, you may need to get a new sensor, repair the wiring, or replace the PCB. That said — don’t just sink money into an old boiler, especially if it’s out of warranty. When the repair costs spiral beyond £500, it makes sense to invest in a new boiler with a long warranty. You can get prices for a new boiler in less than 90-seconds here.

Still Having Viessmann Boiler Problems?

If you can’t find the Viessmann fault code you’re seeing in this article, check out Viessmann’s website. And remember, only Gas Safe boiler engineers can inspect or fix a gas boiler.

If you’d like to explore your options for a replacement boiler, we recommend you check out Heatable. Here’s the quote we got on a brand-new Viessmann Vitodens 100-W, including installation, at the time of writing:

You can fill in Heatable’s anonymous questionnaire and get your own range of fixed price boiler quotes.

What’s Next?

Is there anything we’ve missed? Do you have a question that this article didn’t answer? If so, please leave us a comment below and we’ll get back to you as soon as possible.

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