Rainwater coming through flue into boiler? Anyone seen it?

[ChrisOxford]

I opened up my boiler (Worcester 280RSF) today to change a cracked spark electrode which was stopping the pilot lighting reliably. Nice easy job, and it lights instantly now instead of after a minute of trying.

But after removing the inner casing cover, I spotted large droplets of water dripping off the air distribution plate above the fan and small puddles of water on the flue hood assembly, around the gas valve’s flange which the main burner bolts to and around the CC pressure sensing nipples. The water had then dripped down onto the control box, making a mess of the self-adhesive labels on it. Luckily, there’s been no damage to anything in the control box.

I don’t think it’s water from the boiler as there’s no sign of water leaking from anywhere (including the primary HE) and system pressure is rock-solid at 1 bar. The AAV is newish and working properly. The pipes that run upwards to the rads are fine, and the wall it’s mounted on is bone dry.

The boiler’s been out of action for a few days so there hasn’t been any heat to drive off this moisture.

There was torrential rain here overnight, and so I’m wondering whether this is rainwater coming in. The boiler has the standard horizontal flue option, i.e. one 90 degree bend then about 300mm of flue going straight through the wall to the terminal). It’s a flat-roofed house with no overhanging eaves. The boiler was installed by a Corgi-registered fitter in 1994 and has been serviced annually, though always in the summer in very dry weather.

The combustion chamber always seems to have quite a few little leaves and insects in it when it’s serviced, so obviously stuff does work its way in through the flue.

Cheers.

 

[bengasman]

Water through flue is not unheard of.
Opening the combustion chamber is not really recommended unless you know exactly what you are doing.
Was the servicing done by a pro?

 

[ChrisOxford]

Thanks for the reply, Ben(?).

That's interesting to hear. What usually causes it? Installation error, or a fault developing? How is it overcome?

Seems to be coming in through the outer, air section rather than the central fanned flue.

I really appreciate your safety reminder. I usually confine my repairs to the water/electronic side of things (diverter, W-W HE, expansion vessel, AAV etc.), but I thought the "tracking" spark electrode was too much of a no-brainer to call in a pro for. Turned out it had a tiny brown pin-hole (rather than a crack) in it and was arcing across to the pilot assembly at its base rather than sparking at the tip.

Everything has been re-assembled as per the MI, taking great care to replace all the white silicone sealing strips and washers on the inner casing cover, and tightening the screws evenly and to a sensible torque, and I replaced the main burner O-ring (with WB original part) and checked the pilot union for gas soundness with leak detection fluid.

Obviously, I will call in someone to sort out this latest issue as I know when I'm out of my depth, but if possible, I really do like to know how my own appliances work and what goes wrong with them

Thanks again for replying.

 

[bengasman]

That's interesting to hear. What usually causes it? Installation error, or a fault developing? How is it overcome?

Can be various things, impossible to tell without seeing it.

 

[ChrisOxford]

Understood

What's the usual installation procedure for horizontal flues in buildings like mine where there's no overhanging eaves, just a coping stone that projects about 1" beyond the brickwork which potentially drips straight onto the terminal? Should the standard terminal cope?

Thanks again for your advice.

 

[Agile]

The usual cause is an incorrect angle on the flue!

It should slope downwards towards the outside at about 3 degrees.

It sounds as if yours does not and allows rainwater to run into the boiler.

Tony Glazier

 

[ChrisOxford]

Thanks, Tony, knew I could rely on you for a useful answer

Just got my level out, and with the help of some rusty GCSE trigonometry, I make the slope about 1 degree the WRONG way.

Interestingly, the MI states: "Drill the flue hole at 120mm diameter and ensure that it is horizontal through the wall".

Also noted that the engineer who fitted it never applied any silicone between the terminal and the air duct (not the inner, flue duct), as instructed in the MI.

So looks like an installation error that nobody's picked up for 15 years. Shame about all the unneccesary surface corrosion in my boiler

Will be calling in a GasSafe chap to rectify and do the annual service.

Thanks again everyone.

 

[SimonH2]

Everything has been re-assembled as per the MI, taking great care to replace all the white silicone sealing strips and washers on the inner casing cover, ...

That's more than some pros bother to do. One the boiler in my flat, they seem to have mandatory step to throw away the cover fixing screws. Plus, when they replaced the thermocouple recently they didn't bother refitting the seal properly.

IMO it's inevitable that water will ingress under certain weather conditions -after all it's a pipe sticking out through the wall ! I'll disagree with Agile, I thought the flue was supposed to slope upwards going away form the boiler so that condensation in the flue will run back to the boiler rather than dripping outside. On short horizontal through wall installations, I think the slope is done by having the outer shell horizontal and the inner exhaust angled within it. But on longer runs the whole assembly needs to be angled.

 

[ChrisOxford]

I thought the flue was supposed to slope upwards going away form the boiler so that condensation in the flue will run back to the boiler rather than dripping outside.

I'm no expert (obviously), but I seem to remember reading here that you're correct in the case of condensing boilers. But this is an oldie from 1994ish.

The amount of rainwater inside was quite surprising, an eggcupful at least, I'd say, all over bits that looked like they weren't designed to get a good soaking. Probably no big deal if the boiler's in regular use and the water is evaporated off, but destructive if it's allowed to pool for weeks on end.

Chris.

 

[sooey]

I'll disagree with Agile, I thought the flue was supposed to slope upwards going away form the boiler so that condensation in the flue will run back to the boiler rather than dripping outside.

You thought wrong, it's not a condenser.