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HELP! Viessmann Vitodens 100 Boiler not igniting!

HELP! Viessmann Vitodens 100 Boiler not igniting!
HELP! Viessmann Vitodens 100 Boiler not igniting!

Plumbing Problems: HELP! My Viessmann Vitodens 100 Boiler is not igniting!

Solution: Don't Get Mad, but Flapping around a bit might help!

It would seem that Viessmann Vitodens 100 Boilers of a certain age have a tendancy to stop igniting when they should!

When this problem occurs the boiler will seem to work as normal in detecting that heat is required (i.e. it's switch on and thermostat/dial is in a position where it needs to come on.), sounds will be heard as though the boiler and fans are ready and you may even hear the boiler trying to ignite, but nothing more happens, and after 20 seconds or so it will give up!

After this an 'F5' Fault Code may even appear on the display panel.

The F5 Fault Code is indicating a Pressure Switch problem! Now although the Fault Code may be thrown up by the pressure switch, The Fault itself usually lies elsewhere!

There is a flap inside the Viessmann Vitodens 100 that has a tendancy to get a little bit sticky. Once it gets a bit sticky, the flap begins to fail to open as it should every time the boiler is activated. When the flap can not open, the boiler will not ignite.

The solution is a very simple one, but should only be carried out by an Approved/Qualified 'Gas Safe' Registered Plumber by law. You should in no way attempt to mess with a boiler yourself. Boilers, Boiling Water, Gas and Electricity, are all potential killers or could cause very serious harm. Also it needs to be checked afterwards for any gas leaks.

Once your Qualified Plumber has found the flap, simply cleaning the stickiness off the flap will have your boiler up and running again in no time.

This problem seems to be affecting Viessmann Vitodens 100 boilers once they are a couple of years old. Many of those from around 2007-8 will be affected, it would seem that Viessmann have removed the flap from some later/newer models. (Model shown here is a 2008 one.)

Do not remove the flap though, unless Viessmann have said it is okay for you to do this. The later boilers may have been designed differently.

The stickiness seems to be caused simply by a small build up of condensation mixed with dust or grime that has been collected over time around the seal under the flap, it seems more common in boilers that have had longer periods of no use.

Cleaning the flap is only a temporary solution, so have it cleaned as part of your annual boiler service, others on the internet suggest you remove it completely (but you do so at your own risk!), and some have suggested as a compromise that you remove the rubber seal itself (again, you do so at your own risk!), but removing the seal might be a little difficult due to it's difficult location underneath the flap! but at least it would mean keeping the flap.

Anyway do mention the flap to your 'Gas Safe' engineer, as you will discover that it may save you some time and money, when getting the boiler repaired, as you already know where the problem is!

HELP! Viessmann Vitodens 100 Boiler not igniting!
Viessmann Vitodens 100 Boiler.

HELP! Viessmann Vitodens 100 Boiler not igniting!
Viessmann Vitodens 100 Boiler with the front cover removed.

When this boiler was switched on the fans would begin to operate and the boiler would try to fire up, but after about 20 seconds the boiler would just give up.

The ignition and burner indications on the LCD display would flash up but they would not stay on, indicating an ignition/burner problem, but that could be being caused by anything from water, air, gas, igniter, electric circuit or some other part!

HELP! Viessmann Vitodens 100 Boiler not igniting!
Sometimes the boiler would show 'F5' on the display. F5 is a Fault Code. Having a Fault Code displayed makes things much easier or at least it should!

F5 is the Fault code for a Pressure Switch problem! Although it indicates a problem with the Pressure Switch reading, it could be caused by something else upsetting the reading as is generally the case with an 'F5' Fault Code on the Viessmann Vitodens 100 Boiler!

What is likely to be the problem is a sticky flap located within the boiler, thus having a knock on effect on the pressure switch reading!

HELP! Viessmann Vitodens 100 Boiler not igniting!
Get you plumber to turn off the gas and electric and take a look under the 'pork chop' shaped cover!

Inside there should be a small plastic flap. Get your plumber to switch on the electric (but not the gas). The flap should lift up when the boiler tries to fire up. This one would not.

HELP! Viessmann Vitodens 100 Boiler not igniting!
Using a couple of small screwdrivers to lift up the flap, it was indeed a bit sticky. As was the black rubber seal beneath it.

Cleaning off the stickiness, then trying the boiler again (still with the gas supply turned off)! The flap jumped to life this time, solving the problem.

Putting the 'pork chop' shaped cover back on, the gas supply was turned back on, and as if by magic, the boiler ignited immediately :)

The display also showed the burners were working as they should.

The boiler and gas supply were then checked for leaks / pressure tested and the boiler cover was put back on. (...until next time! but at least once you have had the problem you know what is causing it the next time it happens.)


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