hot water presure

[mikieg]

hi guys, so heres the deal , i've lived in the netherlands for the last 12 years, work here as a self employed builder who occasionally does some plumbing, all relatively easy cos its all mains presure,no cold feed from above, never did any plumbing back in the uk and after all these years have no one to ask back home, hence i'm here.
So last year we bought a house in france, middle of no where, second hand aga with back boiler was sourced, immersion heater with heat exchanger, 28mm copper used to connect aga to boiler so no pump was needed,
first time i had the aga burning we had 70c temp in about an hour after about 2 hours the aga couldnt loose its heat any more and began to boil so i thought the easiest way of cooling everything would be to tap off some hot water, the immersion gets cooler and the aga can loose its heat, sadly it seems 16mm cold feed and 16 mm to taps going to 14mm 1 meter from the taps meant there was no presure ..... you might be able to picture the panic as i desperately tried to prevent my house from exploding, my wife would not have been happy.!.
now that you've all stopped shaking your heads or lifted them from your hands, the question
should the feed and run off from the immersion be 22mm? or can it be 28 feed and 22 run off,
does it matter that the last metre to the shower taps is in 14mm ?
the drop from the immersion is 3.7 metres before going vertical for a meter for the shower taps ?
thanks guys, all help is appreciated
mike

 

[justlead1]

Hi. Can not understand what pressure got to do with the situation. When the hot water cylinder over heated was is your intention to run the hot taps to cool the cylinder to allow the heat generated by the aga to be used/cooled when is heated the now cooler water in the cylinder.

 

[WHPES]

Not sure at the moment as I can't work out your set up from the description you give but if the hot water feeds a shower and it is heated by an AGA, you MUST install a thermostatic mixing valve (the high temperature type as the ordinary ones are only rated to about 80 degrees) or someone could be fatally scalded.

I assume you have a header tank above - Can you get water out of the hot taps OK when the system is cooler?

 

[mikieg]

justlead, yep that was the general idea cool everything down,

WHPES, the shower has a thermotap attached but even when the water is cooler i still have no preasure. the header tank is only 8 gallons, with the cold water feed pipes to the imersion being 16mm, thats where i think the problem lies

this is the system i'm aiming for and with the exception of the centralheating side which will be coming in the summer it looks identical, i just dont have the pipe sizes
http://www.deals4homes.co.uk/images/centheat1.gif

 

[justlead1]

Hi The link wont work for me . I'm still lost.

 

[mikieg]

http://www.deals4homes.co.uk/images/centheat1.gif ,

gravity feed hot water system, with what eventually will be a pump driven central heating system with the water heating coming from 2 wood burners

 

[WHPES]

Link won't work for me either.

Your system could be airlocked. Even with 16mm pipe I would expect some water to flow.

By immersion I presume you mean the cylinder (Immersion heater here is an electrical element which heats water in the cylinder).

16mm is too small for a hot water take-off. Should be 22mm minimum, and all hot pipework should be no less than this.

8 gallon sounds a bit on the small side, but this depends on the mains pressure and flow rate.

If you're finding it overheats from the Aga, a common way to disippate excess heat is to fit one or more radiators on the primary circuit. A heated towel rail in the bathroom is quite common.