Grant Vortex Oil Boiler Exploding

[rcg733]

Wonder if anybody has any ideas?

I have an external Grant Vortex Pro Oil Boiler which worked nicely for a few months, but now it is the habit of just boiling the water within itself.

Last night at 1130pm, the pressure release vessel did it's job and sprayed boiling water around the kitchen. The overheat cutout also tripped on the boiler.

The obvious problem to me is that the thermostat in the boiler had gone, but that has been replaced and we still have the problem.

Any Ideas?

[rcg733]

Yes the pumps appear to be working fine - but I guess this happens when the rad's have shut themselves down with the TRV's

Surely the boiler should stop heating itself up when it gets to the set temperature ( eg 65C), not just keep burning until the water has been vapourised

Well that's what I would hope...

[rcg733]

It is all vented to drain outside, but it can't cope with the volume of steam being generated by the boiler, that blows the pressure relief.

Is it normal for a boiler to just turn it's contents to steam?

[rcg733]

Yes it is an unvented system.

Not sure about automatic by-pass valve - I would presume we have whatever is needed.

Would the lack of any of these things cause the boiler to simply boil it's contents?

Surely the boiler has a thermostat so that once the water within it reaches temperature, it stops providing heat?

[rcg733]

Thanks Guindilias - Yes, we replaced the thermostat, and during normal operation, the boiler fired and when then stop providing heat when the water back into the house hit 55C.

All was well, then last night, off it went again, after steam was released the output from the boiler was 92+C!

Whilst I accept that there may be lag caused by heat retained in the metal which my heat the water within the boiler above the 55C setting, surely, regardless of loops elsewhere etc, the boiler should stop providing more heat which ends up with the water boiling!

I guess my first job is to remove the TRV on the By-Pass rad, but even if that stops the steam, it still appears to me that the boiler is pretty seriously mal-functioning - but obviously I am no expert, hence my post!

[rcg733]

clockworks said:

If the burner is still running after the thermostat has told it to stop, then it does have a problem. Does it actually carry on running though?

What other rational explanation is there for the water within the boiler turning to steam?

There was still steam hissing out of the top of the boiler 3 hours after it had cut off last week!

Of course, when you sit and watch it, it is as good as gold, but then 24 hours later it blows again.