Bathroom rad- Pump required?

[teb532]

I am installing a new bathroom and have the following problem: Our hot water is heated by an aga on a simple gravity loop, however the hot water becomes scalding as there is no means to thermostatically control it. I have researched this problem and there is no simple solution although it is suggested that putting a radiator in the loop would act as a heat sink and therefore reduce the hot water temp.
As I am putting a new bathroom in this seems an ideal time to do this, my plan is to tap into the aga loop where it enters and exits the hot water cylinder and run 15mm plastic through the attic to the new bathroom (at the other end of the house) and into a large chrome towel-rail type rad. I am certain this spur will not work by gravity so I will need to put some sort of pump into it, so my questions are:

1. What kind of pump will I need, is there such a thing as a mini-CH pump since a full sized one is clearly overkill.
2. Is this plan going to work, will pumping the new loop upset the main 28mm gravity loop that heats the hot water cylinder.

Any help / advice much appreciated.

 

[gasmarc]

it sounds like you have no control over your hot water, I would suggest converting the system

 

[teb532]

I agree to a degree - however I have to play the ball where it lies and I cannot convert the entire system. This is a well known phenomenom with agas - One solution to the hot water problem is by fitting a thermostatic mixer valve at the exit of the HW cylinder, mixing in some cold to give a fully controlled hot water temp. However the addition of the towel rail as a heat leak will certainly help - we need a hot towel rail as there is no other heating in the bathroom.
Therefore my proposal (if it works) would kill two birds - help reduce hot water temp (although I concede not fully control it) & provide heat in the bathroom. Even if it only succeeded in the latter I would be satisfied as I can attack the excessive water temp as outlined above.

 

[Robtheplumb]

If you can tee into the Aga flow pipe onder the floor then run your pipe UPHILL to the towel rail you could then take your return from your towel rail up into the loft and join into your aga vent pipe, this would then work on gravity and you shouldn't need a pump. Your towel rail will work better if it doesn't have any baffles in. You would also be better using copper pipe as this will be better at avoiding sagging pipes (not good on a gravity system).

 

[teb532]

That makes sense but does create a couple of problems - To work solely on gravity I reckon it would have to go in 22mm due to length of run which in copper will not be cheap. It also means ripping up the upstairs floor to run the pipes, which I was hoping to avoid, especially since it is a very long run and may well prove to be wasted time if it doesn't work. If there was a simple pump solution that would definitely be my preferred option.

 

[teb532]

Having spoken to the technical department at Wilo pumps and have been persuaded that one of these will work well and although some initial outlay involved should be very economical on electicity:

[DLMURL="http://www.wilo.co.uk/cps/rde/xchg/gb-en/layout.xsl/1188.htm"]WILO (U.K.) Ltd. - Wilo launches most efficient small circulator ever! - Pumpen Intelligenz[/DLMURL]

Not sure if anybody out there has any experience with them but I will let you know if I succeed.