Hi
I've got a Grundfos 1.5-stc positive head twin impeller pump installed for my shower in upstairs bathroom. The 22mm hot feed comes from my hws via the warwick flange which I installed to ensure it had a dedicated feed with as less air as possible. The 22mm cold feed to the pump comes from a dedicated outlet on cws tank in the loft. Both hot and cold outputs from the pump then go up into the loft and down into my shower. I have fitted auto air vents (bottle type) at the highest points in the attic. Also worthy to note is I have installed a 22mm Double Check Non Return Valve on the hot pipe after the pump. Pipework is 22mm speedfit.
Up until now the only way I can get hot to come through is to lower the shower head, turn the Grohe Precision Joy mixer down to cold and then turn on the water flow. Then turning the temperature dial to hot the hot water comes through - with the shower head able to be put back up to its normal mount. The Grohe Precision Joy mixer has built-in non return valves and dirt strainers.
Now having read a number of posts I have realised thanks to 'Richard C' that there is a rule that:
"If the shower head or any part of the pipe work (up & over loops) to the mixer is less than 60cm from the underside of the cws tank you could be in a negative head situation, if your not using a negative head or self selecting pump, you could have problems.
Read more: //www.diynot.com/forums/viewtopic.php?t=170800#ixzz3NrvgSFAw
"
So I'm convinced I've got a negative head setup thanks to the up and over loop I installed. Downside is I realised I'd have to buy another pump and after quite a bit of research I'd probably be wanting something like the Stuart Turner Monsoon Universal twin 2.0 bar which I can only find for cheapest of £405.
Question I have is, if I really do have a negative head setup why does the cold water come through much more readily, compared to the hot water - they both go 'up and over' into the attic?
If I turn the pump off, only the cold water comes through and no hot comes through. Also worthy of mention is I can hear some air coming through the shower head when showering. Not sure if this air is being dragged from the vent pipe above the hws cylinder.
On top of this, we've got a fairly old boiler (F energy rating) and it has got us thinking whether we should avoid buying the negative head pump and buy a combi boiler. From spending an entire day researching it, I'd be looking at going for the "Vaillant ecoTEC Plus 937 Power Store Combi Boiler Natural Gas". However, I'm unsure given the 'up and over' implementation whether that would give me a good enough shower experience despite opting for the max 20 litres/min 37kW model which seems to be pretty good. I do have a very good incoming water mains to the house so don't think that'll be a problem.
I'm trying to ensure I fully understand the situation before investing further and would appreciate any guidance/ideas.
Thanks in advance
I've got a Grundfos 1.5-stc positive head twin impeller pump installed for my shower in upstairs bathroom. The 22mm hot feed comes from my hws via the warwick flange which I installed to ensure it had a dedicated feed with as less air as possible. The 22mm cold feed to the pump comes from a dedicated outlet on cws tank in the loft. Both hot and cold outputs from the pump then go up into the loft and down into my shower. I have fitted auto air vents (bottle type) at the highest points in the attic. Also worthy to note is I have installed a 22mm Double Check Non Return Valve on the hot pipe after the pump. Pipework is 22mm speedfit.
Up until now the only way I can get hot to come through is to lower the shower head, turn the Grohe Precision Joy mixer down to cold and then turn on the water flow. Then turning the temperature dial to hot the hot water comes through - with the shower head able to be put back up to its normal mount. The Grohe Precision Joy mixer has built-in non return valves and dirt strainers.
Now having read a number of posts I have realised thanks to 'Richard C' that there is a rule that:
"If the shower head or any part of the pipe work (up & over loops) to the mixer is less than 60cm from the underside of the cws tank you could be in a negative head situation, if your not using a negative head or self selecting pump, you could have problems.
Read more: //www.diynot.com/forums/viewtopic.php?t=170800#ixzz3NrvgSFAw
"
So I'm convinced I've got a negative head setup thanks to the up and over loop I installed. Downside is I realised I'd have to buy another pump and after quite a bit of research I'd probably be wanting something like the Stuart Turner Monsoon Universal twin 2.0 bar which I can only find for cheapest of £405.
Question I have is, if I really do have a negative head setup why does the cold water come through much more readily, compared to the hot water - they both go 'up and over' into the attic?
If I turn the pump off, only the cold water comes through and no hot comes through. Also worthy of mention is I can hear some air coming through the shower head when showering. Not sure if this air is being dragged from the vent pipe above the hws cylinder.
On top of this, we've got a fairly old boiler (F energy rating) and it has got us thinking whether we should avoid buying the negative head pump and buy a combi boiler. From spending an entire day researching it, I'd be looking at going for the "Vaillant ecoTEC Plus 937 Power Store Combi Boiler Natural Gas". However, I'm unsure given the 'up and over' implementation whether that would give me a good enough shower experience despite opting for the max 20 litres/min 37kW model which seems to be pretty good. I do have a very good incoming water mains to the house so don't think that'll be a problem.
I'm trying to ensure I fully understand the situation before investing further and would appreciate any guidance/ideas.
Thanks in advance
