hot water goes up into header tank

[Mister Dan]

if our hot water is on for over an hour and the water isn't used - it vents from the hot water tank to the header tank in the loft, this happens if the water is heated by the boiler or the immersion heater?? We've tried adjusting the boiler thermostat to low but this doesn't help.

 

[JPC]

seems ur stat on the cylinder has been turned up or is not working ?
and coincidently the stat on ur heater is also to high or broken.
in either case nothing is telling the boiler or element the req. temp. has been reached and boils over

 

[chrishutt]

Unlikely that both thermostats have failed. I suspect that the vent pipe does not rise enough above the level of water in the tank before inverting. Can you hook it up a bit higher? there's usually a bit of play in the pipework.

 

[Mister Dan]

thanks very much, that's a great help, we'll try that.

 

[andyyoung]

does your header tank start to overflow dan? i had a similar sounding problem. the coil in the indirect hot water cylinder had corroded allowing boiler heated central heating water to mix with the pure water coming in from the cold tank. respective levels of cold and header tank meant that water being forced out via header.

 

[Agile]

If the boiler stat was working properly then the boiler output would be limited to about 85*C and the stored water would reach this temperature and the boiler would go off.

If the immersion stat was stuck on then the temperature would rise until the water boiled.

Based on the information given I find it difficult to see that there is a single fault as it seems illogical as stated.

Perhaps there is further evidence? In any case a proper investigation with the temperatures reached at each part of the system would be needed.

Tony

 

[chrishutt]

Tony, my thinking was that if the height between hot water cylinder and feed tank were great enough, the hot (less dense) water in the vent pipe would rise enough above the level of the feed tank water to actually overflow, if the vent pipe invert was low enough. If the information given is correct, that seems to explain everything, does it not?

 

[Agile]

Well I have never encountered that happening and would not expect the difference of say max 4% to be significant to the levels.

However, that suggestion is immediately quashed because one assumes from the posting that its a fault which was never there originally and has only just started to affect the system recently.

Tony

 

[chrishutt]

Tony, If your figure of 4% is about right, a 6 metre head from cylinder base to feed tank water level would give an excess water level in vent pipe of 240mm. If the invert of the vent pipe had formerly been higher, but the vent pipe slipped down due to inadequate fixing (not uncommon) then my scenario would be valid.

 

[ChrisR]

Nice try ChrisH but it's a bit of a long shot! Water only expands about 4% between 4 and 100C.

So maybe 3 cm per metre head. If the vent is ON the top edge of the tank and the water level is awful high and you've got 3 floors of head then it's just possible!

-------------------------------
Crossed your last post - yes vent could have slipped.

Still seems more likely the immersion is boiling the water.

Matt you said HEADER TANK - did you mean the big tank or the small one? If the small then it's MUCH easier to explain!!

 

[chrishutt]

Still seems more likely the immersion is boiling the water.

Yes, but that doesn't explain why it also occurs when DHW heated by boiler, where temps. are limited by cyl. stat and boiler stat. They can't all have failed!

 

[Agile]

Never assume anything!

Multiple faults can happen but are rare!

Most plane crashes are a combination of a minor failure and a human misintrepretation.

Does anyone know of a commercial airline pilots forum? Re Greek crash following a failure to pressurise, I thought one pilot was required to always breath O2 in case of depressurisation?? That did not happen?

Tony Glazier

 

[ChrisR]

Don't you often find that the symptoms reported aren't quite right? I find it always pays to consider the most likely single fault consistent with most of the story, pretty early on. (Hey, I'm agreeing with Tony here!)
Dan says that the water "goes over" even with the boiler turned low, and when heated by the boiler not the immersion. That's only 60C or so, which makes our expansion only about 2%, even less when the tank heats up! (We do need to know the height).

So there is no likely single fault? Recheck the symptoms please.

I did find a really odd fault where an immersion heater was wrongly wired and switched, so it was heating water to boiling (L - E current) even when it was switched OFF. (Reported on gas-news) But I don't expect to see that one again!

 

[Nige F]

I did find a really odd fault where an immersion heater was wrongly wired and switched, so it was heating water to boiling (L - E current) even when it was switched OFF. (Reported on gas-news) But I don't expect to see that one again!

I had a 20 feet deep x10 feet square sewage pumping pit BOILING when the 3 phase board became submerged Never seen or smelled owt like it...didn`t go too close