Generally speaking, this is when a stove, which was working perfectly fine when you last used it, then inexplicably doesn't work. It will be difficult or impossible to light, possibly causing smoke to enter the room. There could actually be a number of causes (see list at the end). However, at certain times of the year when there are dramatic swings in temperature and especially because the problem has occurred suddenly, it is more than likely to be caused by 'spring and autumn syndrome' and is therefore unlikely to be a problem with the stove.

How your flue should work
The stove and its flue uses the temperature differences between the room and the air outside. Under normal circumstances the air inside a home is usually warmer and lighter (because as it warms it expands and becomes less dense) than the colder outside air and this creates a pressure difference which induces a natural updraught inside the flue – where warmer air has to rise up through the flue because it is under greater pressure. This natural draught will exist whether or not the stove is being used and the greater the temperature difference between inside and outside, then the stronger the updraught or 'draw'. This process will be accelerated when hot combustion gases are introduced into the flue thus enabling them to be successfully exhausted into the atmosphere.

Problems occur with updraught when the temperatures are reversed. For example, those days when it is suddenly warmer outside than inside – usually during unseasonably hot spells in spring or autumn. This is when lighting your stove becomes difficult because suddenly there's no natural updraught to kick-start the process. The air inside is colder and heavier than the air outside and this creates a kind of heavy cold 'plug' in the flue which wants to fall back into the room thus creating downdraught. You will probably not know that this is happening until you try to light your stove. Once you are aware of the conditions which cause spring and autumn syndrome however it is actually easy to deal with.

How to overcome spring and autumn syndrome
Prepare your fire, but this time use much more quick-burning kindling than normal and one or two additional firelighters. The Scandinavian 'top fire' method is always to be preferred in these situations. This is where the bigger logs are placed on the firegrate, with kindling on top of the logs and then firelighters on top of the kindling. Ensure the stove's air controls are fully open. The additional firelighters and larger amount of kindling will produce a fast burst of flame and therefore generate heat quickly to help increase the updraught. Do not add any big logs until you are satisfied that the stove is operating normally. At the start you may see some very minor smoke leakage but this should quickly dissipate as the heat inside the flue increases. It is worth noting that all of this can take significantly longer with a boiler stove due to the cold water inside the boiler generally keeping the fire chamber and flue gases at a lower temperature for longer.

Where a stove has a Direct External Air Supply (DEAS) the conditions for creating spring and autumn syndrome are eliminated because the system is 'sealed' and therefore the room temperature (and pressure) should not affect the performance of the flue because none of the colder air from the room is being used inside the stove. Post-2008 homes, which are generally much warmer inside, will also reduce the probability of spring and autumn syndrome.

Other factors
There are many other factors (including attempting to burn wet wood) which can increase the potential for poor updraught and which therefore may also increase the likelihood of spring and autumn syndrome...

• If the flue / chimney is of insufficient height (it should be a minimum 4.5 metres from the top of the stove) 
• If there are more than two bends in the system (90º bends should be avoided except for rear flue connections and they must also have a means of inspecting and cleaning them)
• If the un-insulated single skin connecting pipe is greater than 1.5 metres this will potentially reduce the all-important flue gas temperature at the exit
• If the chimney or flue system is on an external wall and / or is subject to a prevailing wind then flue gases will cool very quickly
• If there is a possible blockage in the flue system (eg bird's nest) or in the stove's flueway (the area above the baffle plate). With Ecodesign's drive to reduce emissions and many new models now featuring double baffles we foresee that flueways will be easier to block especially for stove owners who don't regularly inspect this area, who don't annually service their stove and burn unseasoned wet wood 
• If there is an insufficient air supply to the room so that a stove which doesn't have a direct outside air supply is 'starved'. All stoves in post-2008 houses require a dedicated air vent. In houses built before 2008 (provided the air permeability hasn't been upgraded to post-2008 standards) only stoves with a heat output of more than 5.0kW require them. 
• If the room's dedicated air vent or direct external air inlet is blocked (eg snow drifts, leaves etc)
• If there has been significant tree growth near the flue exit. A new building extension or new neighbouring building can also reduce the effectiveness of the updraught. 

These important topics are discussed in other FAQs on The Stove Yard website.

IMPORTANT: Never use your stove if smoke continues to enter the room. Please seek professional advice and do not use the stove again until the problem has been identified and rectified. See our FAQ on stove emergencies.