Boiler fires for a few seconds then stops. Or won't fire at all. Often there's a gurgling or bubbling from it as it tries. Nine times out of ten in a cold snap, and regularly the rest of the year too, it's the condensate.
There are two places it goes wrong and they're very different jobs. One you can usually sort yourself in twenty minutes. The other needs someone. Here's how to tell which you've got.
Not sure it's the condensate at all? Start with the six first checks.
Modern boilers pull extra heat out of the exhaust gases, and doing that produces water. It has to go somewhere.
That's the condensate pipe. Usually white or grey plastic, about the width of your thumb, running from the bottom of the boiler to a drain. Sometimes it goes to an inside waste, which is ideal. Very often it runs out through a wall and down the outside of the house.
Inside the boiler there's also a trap, which does the same job as the bend under your sink. That can block too, and that one has nothing to do with the weather.
The water in it is slightly acidic, so it also eats metal fittings. If there's metal in that run, it's wrong.
Go outside and find the pipe first.
Points to the outside pipe:
Points to the trap inside the boiler:
Either way you'll often hear a gurgling or bubbling from the boiler when it tries to fire.
The outside pipe you can usually deal with. The trap is inside the boiler, so that one isn't a job for you.
Fill a jug or a watering can with warm water. Not boiling.
Pour it slowly along the outside pipe, starting at the end and working back toward the wall. The blockage is usually right at the end, at a bend, or wherever the pipe is most exposed.
A hot water bottle, or a cloth wrung out in hot water held against the pipe, works well too and is gentler on it.
It normally takes a few goes. Give it ten minutes and try again.
If it's muck rather than ice, warm water sometimes shifts it and often won't. Don't spend all morning on it.
Don't use boiling water. It can crack the plastic, it can scald you on a cold slippery morning, and it refreezes quicker than warm water does.
Don't go up a ladder in ice to reach it. I mean this one. If the pipe is up high or on a first floor, that's the point to ring someone rather than climbing in freezing conditions. A boiler repair is cheaper than a fall.
Don't take the boiler casing off. Everything you can safely do here is outside the boiler.
Once you've warmed the pipe right through, give it a couple of minutes and reset the boiler. Once.
If it fires and stays running, that was it.
If it doesn't, have a feel along the pipe. If any of it is still cold to the touch, or you're just not sure it's fully thawed, give it more warm water and try again. No harm in that at all.
What there's no point in is hitting reset over and over without doing anything in between. If the pipe's properly thawed and it still won't hold, something else is going on.
A condensate that goes every winter, or blocks up every year or two, is usually telling you something about how it was run.
Most often one of these:
I won't pretend it's always the installer's fault though. Sometimes taking the condensate to an inside drain means lifting floors across half the house, and nobody's doing that for a boiler swap. An external run is often the sensible decision, agreed with the customer at the time.
And in a genuine sustained freeze, somewhere around three days of proper minus, even a well run pipe can go. We don't ban outside condensate runs in this country the way colder ones do, so most of our housing isn't set up for the real extremes. Rare, but it happens.
So the question isn't whether the pipe is outside. It's whether it was done properly. Decent fall, a size up on the bore, lagged, terminating somewhere sensible. Done that way it'll see you through almost every British winter, and it won't be blocking every other year either.
Depending on which of those it is:
Worth knowing before anyone quotes you. Thawing it out gets you going again and that's a fair job to pay someone for. But if it's the third winter running, you're paying to fix the same thing every year, and one of the above is what actually stops it.
Most makes report this as a flame or ignition fault, because that's what the boiler sees:
Codes shift between models and ranges, so check yours against the manual if it isn't listed. A code naming ignition or flame loss in the middle of a cold snap should have you outside looking at that pipe before anything else.
That last one especially. If it's happened more than once, the question is how the pipe is run rather than what's wrong with the boiler, and that's worth knowing before you pay someone to warm it up again.
If it's the pressure dropping rather than the boiler cutting out, that's a different fault.
And if it's a hard frost and you're stuck without heating, there is a temporary way to keep the boiler running until the weather breaks. It's straightforward enough, but it needs doing properly and it needs someone watching, so it's a call rather than a paragraph on a website.
I'm Carlo Cennerazzo, twenty-three years in the trade. Point your phone at the boiler and I'll go through it with you, tell you what's wrong, whether you can sort it yourself, and what it should cost if you can't.
£20, no callout charge, same day when there's a slot free. A written report follows afterwards, so you've got it in black and white rather than trying to remember.
And if you've already had someone out and you're holding a quote you're not sure about, that's worth a call too. I've no interest in who does the work, so I'll tell you straight whether the price is fair and whether it's even the right job.
Don't book a call. Leave the property, then ring the National Gas Emergency Service on 0800 111 999. In Northern Ireland it's 0800 002 001.