Boiler Issues - not sure what's wrong and charges for fixing it

[ollski]

Only lose half if the water somehow doubled in volume when heated, otherwise the expansion vessel would have to be bigger then the cylinder!, and the remaining water would still be there and hot enough surely anyway?

wouldn’t that assume that the lost water isn’t being replenished?. Are you calculating that on the original volume or the total volume and over what time period?

 

[John D v2.0]

wouldn’t that assume that the lost water isn’t being replenished?. Are you calculating that on the original volume or the total volume and over what time period?

Yes it would assume that. Are you expecting replenishment? The water is only being lost because it's going out the relief valve. Assuming we are still talking about a faulty EV, the incoming water pressure from the reducing valve would be lower than the set pressure of the relief valve. Therefore no replenishment would happen.
I'm calculation over however long it takes to go from stone cold to whatever the thermostat is on eg 60c.
Obviously when water is used cold will enter, but i don't think anyone would expect otherwise!

 

[ollski]

This is true on paper, just never worked on paper. In real life the timer goes off the water contracts and the cylinder refills with stone cold water.

 

[Gasguru]

Er..water is virtually incompresible and you don't need to heat it much for the pressure to rocket and open the expansion relief valve.
It's very common in London to find the tundish completely blocked with scale from a constantly dripping relief valve....and as with all relief valves once they've opened it's a short time before they stay open even if the pressure drops below the set pressure.

 

[ollski]

Now there is someone that really does not know how a sealed hot water system/security group set works, the relief valve is normally set to seven bar and would only open when the water pressure exceeds this, in normal operation a five litre bucket would fill in about six months, when heating every day.

Are you suggesting that 3 bar of water pressure in a sealed container being heated by maybe 40/50 degrees will struggle to hit 7 bar??

 

[ollski]

Wow, the price's have really dropped since I last bought one, in France they are about twice the price now, but seven years ago I paid €139,00 for one in Leroy Merlin, thanks for pointing that out, trouble is the reviews on LM site say theirs are only lasting a few months to a year.

Not familiar with that particular brand but on many potable water expansion vessels you can replace the internals. Rarely worth it in the UK due to price

 

[Dan Robinson]

Now there is someone that really does not know how a sealed hot water system/security group set works, the relief valve is normally set to seven bar and would only open when the water pressure exceeds this, in normal operation a five litre bucket would fill in about six months, when heating every day.

You are talking arse.

 

[ianmcd]

Very rarely have I read so much shoite in one post, it does happen now and then, but some here are taking it to a whole new level.

 

[Gasguru]

WTF

 

[Dan Robinson]

FFS

 

[ollski]

I’m going to bow out and brush up my G3

 

[Dan Robinson]

Yeah - and go and tweak some TPRV's whilse you're at it

Unreal.

 

[John D v2.0]

This is true on paper, just never worked on paper. In real life the timer goes off the water contracts and the cylinder refills with stone cold water.

Good point that it would effectively cool quicker due to gaining cold water instead of air expanding. however you did specify"every time" it's heated it would lose half and be tepid, actually that would just be over longer periods of time. Although the cylinder would still reach temperature fine, it would just waste a lot of hot, and cool quicker.

 

[ianmcd]

Not at all, I said that the bucket fills, it hits seven bar every heating cycle momentarily and releases water into the bucket through the safety release valve.

well it shouldnt

 

[MeldrewsMate]

...The internal bubble is just an internal expansion tank, a membrane at the top of the cylinder that separates the water from a void this has to be charged, no difference in reality.

Mike

Mike, the reality in this case is that the internal bubble is a fixed volume of air trapped at the top of the cylinder by virtue of a depressed dip-pipe on the cylinder's hot water outlet. It can only be filled at atmospheric pressure by the user (following the user instructions), and cannot be overcharged.
Compare that to an external EV which the unsuspecting user re-charges to 6/7/8/bar or more, thus rendering it useless at best, possibly rupturing the diaphragm and facilitating a water leak, and even causing a catastrophic failure (explosion) of the EV shell in a confined space at worst.

To say there is no difference in reality is just wrong.

I've had people looking over my shoulder when working, and it all looks so simple. "Is that all it was?" I hear very often, but in fact it is the actions I would have taken if something had gone wrong that set me aside from the unskilled/unfamiliar/ignorant.