Discuss can someone please clear up my pressure and flow issues with unvented cylinder? in the Plumbing Jobs | The Job-board area at PlumbersForums.net

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ecswtrav

Hi all, this relates to a previous problem ive posted here before. Without going into too much detail, I have an unvented cyclinder boiler (ideal istor) that up until now had been delivering measly flow rates of 8LPM max and if I ever attempted to run 2 showers at once one of them would become unusable. I had my mains pipe changed to 25mm around a year back and still no difference.

Anyway, just recently I determined that where the pipe enters the property it is instantly reduced to 15mm and has a PRV attached with the cold and hot pipes after the PRV. The boiler/cylinder is fed with 15mm but the hot pipework leaving it is in 22mm. The cold throughout the house is 15mm.

Having noticed this I've had the 15mm piping upgraded to 22mm with a new PRV installed still set at the recommneded 2bar. As a result the flow rates with the hot are much better - around 15LPM and I can run 2 showers are once with minimal drop off.

The only issue I have now is that the 15mm piping for the cold delivers a much slower flow rate at all outlets in comparison with the hot. I've simply put this down to the fact the hot is 22mm but then cant figure why the hot becomes 15mm on a short run to the showers/taps etc. So, to me every outlet is 15mm although the hot travels a good distance at 22mm.

Would the 22mm run for the hot (reduced to 15mm at the outlets) give better flow rates than a 15mm run throughout for the cold?

I'd love to know why I have different flow rates yet the cold is off the PRV just like the hot pipe? If anyone can clear this up I'd be very grateful.

If my previous unregistered thread can be deleted please...posted it thinking I was logged in!
 
Theres nothing hidden away on the cold pipework after the prv?
 
No, I've fololowed the pipework as far as I can before it goes up the wall and I can see anything other than elbow joints. I wondered if there was something else causing the restriction but again thought it was simply down to the 22mm pipe. Could this be the case?
 
The cold outlets are definitely off the mains? Had a job a couple of weeks ago that all upstairs cold turned out to be tank fed from the loft.
 
100% off the mains Simon. Both the cold and hot supply are limited by the PRV so they are both at 2 bar. If I increase the bar on the PRV the cold flow increases but so does the hot in proportion...and the tundish starts dripping so I have to turn it back down to 2bar.
Is cold piping alwatys 15mm in a house?
 
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