Blog>Expert Advice>Viessmann boiler problems: common issues and how to fix them
Last updated: 8 November 2024
Viessmann boiler problems: common issues and how to fix them
Every boiler can be temperamental. If you're struggling with a Viessmann boiler, don't worry. It may be something simple. Discover the most common problems – and when to call in a professional to fix them.
Many homeowners (and heating engineers) rate Viessmann boilers for their durability and energy efficiency when it comes to heating our homes.
However, issues do crop up. Just like any essential household appliance, working hard behind the scenes 24 hours a day. This is especially true with older boiler models.
This guide helps you troubleshoot the most common Viessmann boiler problems – and how to fix them.
Your Viessmann boiler problems explained
Rule number one for keeping your Viessmann boiler working efficiently is an annual service by a qualified heating engineer. This makes sure your boiler is working efficiently and keeps your warranty validated.
However, even the most well-maintained boilers will experience the odd malfunction from time to time. Some of the most common issues with Viessmann boilers are:
Low pressure
Error codes
Odd noises or vibrations
Programming out of sync
The pilot light going out
Faulty fan
The good news is, with a bit of know-how, some of the issues above could be a DIY fix.
However, other jobs require a qualified heating engineer. Fiddling with gas and electrics can be extremely dangerous in inexperienced hands.
Read on to figure out which jobs to tackle yourself – and which to leave to the professionals.
What to do when an error code is displayed
Error codes are a handy way of quickly troubleshooting a problem – but only if you know what they mean!
If you've misplaced your manual, here are some of the most common error codes for Viessmann boilers – and what to do about it:
F4 - Flame loss
This means the boiler does not have a flame signal or a lack of flame.
Frustrating as it may be, your boiler will most likely lockout (or be turned down significantly). This is a safety measure to keep you safe and prevent any damage to your boiler's internal components.
First, check that it’s not an issue with your gas supply rather than the boiler itself. Contact your utility company directly or ask your neighbours if they are experiencing the same problem.
If that’s not the answer, it could be a faulty flame sensor or a buildup of carbon on the flame sensor. Both of which need to be looked at by a heating engineer.
F5 - Flue blockage or fan fault
This points to a problem with the boiler’s fan or a blocked flue (the pipe found outside your home that safely removes gases from your boiler).
Checking to see if something is blocking the flue is your first step. Look out for other signs of a blocked flue, including a strange exhaust fume smell or a black substance building up around the flue.
However, looking for a blockage in your boiler's internal fan is trickier and needs to be carried out by a qualified heating engineer.
F10 - Low system pressure
This means there’s low pressure (a similar issue applies to the F1 error code), and it is often caused by incorrect radiator balancing or insufficient water in the system.
Checking the pressure gauge and re-pressurising the system if it’s below 1 bar is relatively straightforward, with a bit of know-how.
However, if the pressure drops repeatedly (even when you’ve re-pressurised it), you’ll need a gas-safe engineer to check for a leak.
Top tip – The list above only covers some of the most common Viessmann fault codes homeowners experience. For an extensive list of all the error codes, the Viessman website has a handy online fault code finder.
What to do when no error code is displayed
Sometimes, a Viessmann boiler will show no error codes, but it doesn't take a genius to work out your boiler is on the blink.
Standing under a freezing cold shower or coming home to a chilly home with no heating is a surefire way to know your boiler isn’t working as it should.
To diagnose what the problem could be, you’ll want to investigate the following:
1. Check your boiler pressure
As mentioned above, low boiler pressure can happen if you have not balanced your radiators correctly.
As a general guide, the typical boiler pressure is between 1 and 1.5 bars. Anything lower than this will likely require repressurising your boiler.
Luckily, this is a relatively easy fix. To check your boiler's pressure, follow our comprehensive guide on repressurising your boiler.
Top tip: Remember to check your manual for any extra steps you might need to take depending on your Veissmann boiler model.
2. Check for airlocks
If you’ve checked the boiler pressure and that’s not the issue, it could be because air is trapped in your boiler’s system.
The easiest way to release the air is by bleeding out your radiators.
You could also try using a hose to force water through the system and push the air out. However, this is best left to the professionals.
3. Check for a faulty diverter valve
Diverter valves work hard to direct hot water from heating systems to our home’s radiators, taps, showers, and underfloor heating.
If one of them becomes stuck, you’ll soon know about it. At worst, your heating might start coming on without hot water. Or you'll have inconsistent water temperatures, making your morning shower a little dicey.
A stuck or faulty diverter valve can only be repaired by professionals. That's because you're dealing with a vast network of wiring and gas components which could be dangerous in inexperienced hands. Try fixing it yourself, and you could also invalidate your boiler's warranty.
Our expert advice guide about freeing a stuck diverter value covers the costs involved.
See the tradespeople we've checked and recommend for your job
4. Listen out for strange noises and vibrations
Hearing quiet whirling and clicking sounds is common with any household boiler.
However, loud banging, whistling, gurgling or vibrations coming from your Viessmann boiler isn't normal and could be a sign of trapped air or pump problems.
As explored earlier, the air in the system can be easily fixed by balancing out your radiators.
However, a faulty circulation pump will need fixing by a professional. If ignored, it could cause irreparable damage.
5. Check your pilot light
It sounds obvious, but don’t forget to check if your pilot light has gone out.
It could be an issue with your electricity or gas supply rather than a fault with your boiler.
Before you do anything, you’ll need to check if your boiler has a manual or automatic pilot light. If unsure, your instruction manual will have this information.
If you have an automatic pilot light, you MUST NOT try to light it manually.
Our expert advice article provides plenty more information about the steps to take if your pilot light has gone out.
6. Check your thermostat and timer
There’s nothing more frustrating than a boiler running at the wrong temperature or the wrong time of day.
A broken or incorrectly set timer or thermostat can often be to blame, and luckily, it’s a fairly simple fix.
First things first, check that your timer settings haven’t been accidentally set to a different mode, like an eco-setting.
If you have an older Viessmann model with a analogue thermostat, you can also check if the inside needs cleaning. You can do this by turning off the power, removing the thermostat cover, and gently removing any surface dirt with a soft-bristled brush or cloth.
Still no joy? Then, it could be time to replace the thermostat. This job requires electrical wiring and safety know-how and is best left to the professionals.
How to find a heating engineer to fix your Viessmann boiler problems
Search for a professional to repair your Viessmann boiler safely and efficiently by following these three simple steps:
Use a professional directory
Save time by using a professional directory (like Checkatrade!).
We're so confident in the quality of the trades on Checkatrade that if you book through us, we guarantee their work up to £1,000. Guaranteed for 12 months – Eligibility criteria and T&Cs apply.
Contact or pay a trade through Checkatrade and you’re covered by our 12-month guarantee of up to £1,000*
Read online reviews
A review from a previous customer is one of the best ways to check a tradesperson's professionalism.
At Checkatrade, we check all online reviews to ensure they're from real people and that trades meet our high standards.
We check the reviews on Checkatrade are from real people, and that trades meet our high standards.
Compare quotes
Get at least three quotes from experienced heating engineers. That way, you can be sure you're getting the best tradesperson and price for the job. Search your postcode to get started.
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How much does it cost to repair a Viessmann boiler?
Finding replacement parts is relatively straightforward with a Viessmann boiler. That’s because despite being a German boiler manufacturer, there are many service centres dotted about the UK.
You’ll also find many Checkatrade-approved tradespeople are Viessmann-recommended – so they’ll confidently know their way around your boiler model.
How much a Viessmann boiler repair costs depends on the fault. However, as a general guide, a heating engineer typically charges an average hourly rate of £65 + repairs & parts.
Meanwhile, the average boiler service cost ranges from £100.
However, if your boiler is ten years old or more and the repair costs are adding up, it might be time to invest in a new one. Many utility companies offer boiler payment plans to help spread the costs. Shop around and get a plan that requires no deposit and offers 0% interest for the first three years.
Top tip – If your boiler is still under warranty, you might be able to have repairs carried out for free. Check directly with Viessmann for more information.
Ready to get your boiler (and heating!) back on track? Book with Checkatrade today for reliable, trusted tradespeople.
Viessmann boiler problems: key takeaways
Viessmann boilers are rated for their durability and energy efficiency
Finding replacement parts is relatively straightforward
Only a professional heating engineer can fix the internal components of a boiler, though some DIY fixes are possible
The average boiler service cost ranges from £100
Viessmann boiler problems: frequently asked questions
What is the life expectancy of a Viessmann boiler?
Viessmann says you can expect one of their boilers to last 10–15 years. This is the typical shelf-life for most standard household boilers.
Is Viessmann better than Worcester?
Some homeowners prefer to use Viessmann boilers as they offer longer warranties (seven years). In contrast, Worcester boilers tend to have a five-year guarantee as standard.
Do Viessmann boilers come with a warranty?
Many Viessmann boilers come with a comprehensive seven-year parts and labour warranty (depending on the make and model). You can also extend this further for an additional cost.
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