Boiling water pouring into header tank.

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Mum had boiler serviced today. Called me a few hours later as boiling water coming out of an overflow. Had a look in loft and it's gushing from vent pipe into heating header tank.

It's an old gloworm hideaway, with pumped heating and gravity hot water, no tank stat.

After a bit of "fault finding" I realised that the cylinder was boiling because nothing was turning the boiler off when the heating was on but satisfied - I'm thinking this is down to the boiler stat?? I turned this to "off" and the boiler carried on running!! - removed the stat from its mount and had a waggle - don't know whether it was the electrical connections or the copper tube but it suddenly started working, I put it back and it seems ok for now - I don't know how these work or fail but I suppose it's reasonable to need a replacement after 25 years? I haven't said anything to the engineer as I presume he may have just disturbed it a bit or something and this was just the final straw for it? - and he's actually a mate of mine.
 
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The hideaway stat phial should sit in a pocket on the front
Yes, that was there ok, held in by the split pin/disc, it's the other end where the thin copper tube goes into the control knob housing that I think the issue was.
 
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Mum had boiler serviced today. Called me a few hours later as boiling water coming out of an overflow. Had a look in loft and it's gushing from vent pipe into heating header tank.

My son had exactly the same thing after a boiler service.

https://www.diynot.com/diy/threads/...-after-service-what’s-gone-wrong-here.570542/

The engineer had left the boiler setting onto max. It had always been set on around 75% so something wasn't right but turning it back down sorted it. It's a rental property.
 
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Even if it was heating up it should not cause it to come out of the overflow as the cistern tank should cater for the expansion of the hot water. suggest you alter the float valve in the cistern tank so the top water level in the tank when the ballcock stops flow is 100mm above the tank bottom
 
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Even if it was heating up it should not cause it to come out of the overflow as the cistern tank should cater for the expansion of the hot water. suggest you alter the float valve in the cistern tank so the top water level in the tank when the ballcock stops flow is 100mm above the tank bottom


Won’t make any difference
 
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Could be steam entering at the bottom of the vent pipe and exiting from the top of the vent pipe, some of the steam will condense in the pipe and blown into the header tank as very hot water.

It needs properly fixing ( not a work around ) especially if the tank is plastic as hot water in a tank can result in the tank walls and base softening, distorting and splitting and then very hot water comes through the ceiling
 
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Could be steam entering at the bottom of the vent pipe and exiting from the top of the vent pipe, some of the steam will condense in the pipe and blown into the header tank as very hot water.

It needs properly fixing ( not a work around ) especially if the tank is plastic as hot water in a tank can result in the tank walls and base softening, distorting and splitting and then very hot water comes through the ceiling

I wold be getting a long stick to check for a blockage at the cold feed junction :sneaky::sneaky::sneaky::sneaky:
 
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It was boiling hot water gushing out of that top pipe, the tank was full of boiling water, it was boiling over the top of the tank, the hardboard lid had dissolved and the loft was like a steam room.

I don't know whether it was waggling the spade connectors on the thermostat "box" or the copper tube where it enters the box but until I did that the burner was running continuously, even when I switched the dial on it to the off position - it's only a positive wire in and out so most have been jammed/shorted on.

A waggle in the right place and it's running perfectly now - I'm finding it difficult to "blame" my htg engineer for this.

I'll be replacing the stat as a precaution. I'm just wondering if I should fit a tank stat as well, both as a cost saving and an additional safety check? I'm not sure I understand it but if water had come through the ceiling and we'd turned the water off there would have been nothing to stop the boiler "melting"?
 
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Numerous people have died when the thermostat in their immersion heater failed in the on position. The boiling water vented up to the header tank which then sent boiling water in to the main water tank. Being made of plastic, the 100(?)L tank then spewed the boiling water on to the unfortunate people in the room below.

I am not a plumber but I believe that (newly fitted) immersion heater elements are now legally required to fail in the off position.

Just one of many horrific cases

http://news.bbc.co.uk/1/hi/england/somerset/7175037.stm
 
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Perhaps fit an overtemp stat to the boiler outlet piping rather than in the tank?
It could be wired in series with the boiler stat.

Better at the boiler than the tank i would think.

I wouldn't replace the stat in isolation. I'd also check or just replace the wiring and connector as well.

I'd ask your mate for advice before doing so though. Best be safe.
 
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