myson controller pump 3 port??

[mrmoo]

hi, on a recent job ive found a pump thats different to say the least... myson controller pump... similar to the comet 2 from what i can see... 28mm in 28mm out 3/4 bsp female threaded body and theres a female thread, fitting and 15mm tube coming from the top of the body... what does this 15mm pipe do? it seems to be on the pressure side... my guess its a bypass, but what else does it do to warrant costing 5 times the cost (£250) of a standard grundfos? the system its fitted to is a bodgeit & run system microbore and 15mm, 20 rads approx runs 2 pumps 1 standard and the 3 port pump (3 port nearest the boiler)... it is used in front of a standard pump.
any help would be greatly appreciated as sooner or later this pump will need replacing, and if i can replace it with a standerd pump and cap the top pipe. I haven't had the opportunity to lift the customers floor to trace this pipe

 

[twgas]

IIRC the centre port of the controller pump is like a HW port on a diverter valve

 

[namsag]

Do a google on old smc systems and it will give you an idea , usually there are 2 pumps though. but as twgas says that pipe is more than likely HW

 

[mrmoo]

thanks all for your help... although I had stumbled across SMC systems earlier today and it all made sense (stupid damn idea though as there is always the factor of thermosyphon going on in the HW circuit... Ill have to see whether the customer wants to pay £300 odd for the new pump when it eventually fails of whether its going to be a better option for him if I modify the system and put a stat controlled 2 port valve in or similar (not thought about how id modify it yet... simple enough tho )

Thanks again