Mystery catastrophic combi boiler leak

[bureaucrazy]

Hello, The other week was below freezing weather, so I put the heating on my combi boiler.
The timer was set to come on 15min per hour overnight.

In the morning, I went into the kitchen to find the boiler was dead, about 3 to 5 litres of water on the floor beneath the boiler and the kitchen mains circuit was tripped.

Engineer came out and opened front cover and more water poured onto the floor (imagine a goldfish floating out, etc!)

The upper and lower sections of the boiler are divided by a metal tray (full of water). Above the tray the main parts are only the main heat exchanger, the fan and an expansion vessel. The rest of gubbins are below the tray.

After the boiler was dried out, he put it back together and it has been working OK. He is due to return to check it is still ok.

His theory is that something above the tray got blocked and some part that is normally water tight gave way under pressure and flooded the boiler, only to reseal itself.

The window was open over night and the radiatior was off, so the room got cold but I'd be surprised if it was cold enough to freeze the boiler (as it was on once an hour).

Has anyone seen this happen before or know the likely cause?

I'm just worried it could happen again as the cause has not been confirmed and would like to suggest any answer here when he comes back to check it over again.

Boiler is Baxi platinum combi HE

Thanks

 

[ShaunCorbs]

Was there still pressure in the heating system eg guage still in the green ? (While the puddle was there )

 

[bureaucrazy]

In the morning there was a puddle under the boiler and the pressue gauge was at zero. When the engineer came, he opened the fill loop to see if he could see where the leak was coming from, but no more water came out and it held pressure.

 

[bureaucrazy]

Checking another thread Combi Boiler water leak. | Boilers | Plumbers Forums - https://www.plumberstalk.net/threads/combi-boiler-water-leak.132393/
Another person might have water leaking from flue as on their boiler pressure had not dropped. Not the case with mine. Pressure was at zero and flue has been fine for many years.

 

[Chuck]

If I'm thinking of the right model, the original diverter valve is plastic and has a reputation for leaking; the replacement is brass. If the boiler is not in warranty, Baxi have a fixed price repair. It's relatively expensive (IMO) at around £450 but worth considering if your engineer isn't sure what the problem is.

 

[bureaucrazy]

The diverter valve is brass and is below the metal shelf/tray that divides theupper and lower half of the boiler. As the shelf was full of water, the leak must have come from the upper half.

One note on pressure. There is a very slow drip from the pressure release pipe outside losing about 0.25bar per day.
The boiler has been slowly losing pressure for several years, so I git used to topping it up every week. I don't know if it is all attributed to the pressure valve or another cause as the engineer only noticed the outside pipe drip the other day.

With the boiler topped up, there is no obvious leak inside and the tray was dry but the cover was put back on since.

 

[DevsAd]

Silly Q - you do now have a large basin and/or towels sitting under the boiler?

That is bizarre, and obviously worrying. As you say, there's few 'system-water' components above that dividing shelf, other than the MainX and the two pipes supplying it. Any longer-term leaks from the pipe connections would surely have evidence on it - scale, stains, etc? But there's no trace?

Other than invisibly-split pipe connectors to the MainX, there's only two remotely-likely options I can think of, both involving a split MainX. An external split, opened by the temp/pressure increase of a running boiler, would do this, but you'd now expect it to occur every time the boiler was brought up to temp. Or, a sizeable internal leak may have been large enough to overwhelm the condensate pipe coming from the MainX to the trap below, and cause it to overflow? But, only the pipe is above this dividing tray? Unlikely.

On a different note, your daily 0.25bar loss is significant, and should really be tackled. It'll also mean there will now be next-to-zero inhibitor in your system water, coupled with regular air-infused water doses = corrosion of your rads.

What level do you repressurise your boiler to? And what happens to that pressure as your boiler is turned on for CH - where's it at after, say, a half-hour?