Shower issue - do I really need to replace my hot cylinder?

[pooksahib]

Hi. My bungalow has just had an extension added. The builder reckoned that a Trevi Boost shower would be best (a mixer that uses the 'Venturi' principle). Unfortunately, the shower is not hot enough. I now have two different plumbers offering two different solutions:-

1) fit a normal mixer shower and replace the vented hot cylinder with a pressurised cylinder.
2) fit a normal mixer shower and add a pump.

Plumber 1 says the pump would be problematic - something to do with being too near the vent pipe/sucking in air.

The new hot pipe has been taken from the top of the hot water cylinder up into the loft, along 7 metres then down to the new shower. (It was not possible to put the new pipes under the floorboards.) The cold tank is in the loft, about a foot off the joists and right above the hot cylinder.

Does anyone have any views as to which solution is best?

Thanks in advance.

 

[ajstoneservices]

A pump now and you can keep the Trevi.

 

[seco services]

install the trevi properly then it will work ok.

 

[RigidRaider]

Plumber 1 doesn't seem to know that you can get a special fitting for the top of your cylinder that will prevent cavitation when a pump is used. Can't remember what the damned thing is called though.

 

[doitall]

Pump and an Essex flange is idea.

The pump would need to be a negative head type, and stand somewhere near the base of the cylinder.

 

[kevplumb]

Plumber 1 doesn't seem to know that you can get a special fitting for the top of your cylinder that will prevent cavitation when a pump is used. Can't remember what the damned thing is called though.

View media item 14782
surrey flange

 

[bathstyle]

No need for a negative head pump here, as for the best choice, an unvented is better but it boils down to budget and what other requirements you have

 

[doitall]

The new hot pipe has been taken from the top of the hot water cylinder up into the loft, along 7 metres then down to the new shower. (It was not possible to put the new pipes under the floorboards.) The cold tank is in the loft, about a foot off the joists and right above the hot cylinder.

I disagree Bathstyle, a positive head pump probably wouldn't get enough flow to activate the switch.

 

[bathstyle]

The vast majority of Cold Cisterns fitted in a domestic property are about a foot off the loft joists, at least (which is the case here)

I must have fitted what must be well over one hundred shower pumps to properties over the years, all with the pumped H & C's travelling up in the loft. The flow switches are triggered just fine.

Unless I have missed something, I stand by my statement.

 

[JayJay1978]

I don't know doitall, I've never known Bathstyle to be wrong, or yourself for that matter!!

So who's right?

My understanding is that a negative head pump is only needed if there's only about 6 inches from the showerhead to bottom of CWS tank?

The op said the Trevi boost wasn't hot enough, is this because of the long pipe run (heatloss) or is the cold mains pressure too high?

 

[bathstyle]

Stuart Turner recommend no less than 100mm from bottom of cistern to shower head, this is a little close for my liking and often quite unlikely to happen in a domestic property. There's a little bit more to it than figures like that though, it has more to do with flow rate, you can have a fantastic head of water there but if the shower dribbles out then the flow switches simply wont trigger.

 

[picasso]

has anybody checked the temperature of your stored hot water?

 

[seco services]

The op said the Trevi boost wasn't hot enough, is this because of the long pipe run (heatloss) or is the cold mains pressure too high?

9/10 times a trevi boost will be to cold due to cold mains pressure above 3 bar or nrv's not been fitted.

 

[steve32]

has builder fitted 15 or 22mm hot supply these showers need a 22mm hot supply with a check valve fitted and 15mm cold mains supply min 1.5bar pressure.
if you check mi's i think you need a min hot head height of .5bar and you must use shower head supplied as this will affect temperature.
you cannot fit a pump or un-vented cylinder on this shower.

 

[pooksahib]

Many thanks for all the replies. To answer the points raised:-

"install the trevi properly then it will work ok." I'm confident that it has been fitted properly bar the layout of the hot feed (should be under the floorboards but that was impracticable.)

"The op said the Trevi boost wasn't hot enough, is this because of the long pipe run (heatloss) or is the cold mains pressure too high?" The mains pressure was measured at 4.5 Bar. A limiter was then fitted to reduce it to 2 Bar but that had no effect on the shower temperature.

"has anybody checked the temperature of your stored hot water?" I've had it as high as 65. Don't want to go any higher.

"9/10 times a trevi boost will be to cold due to cold mains pressure above 3 bar or nrv's not been fitted." NRV's are there.

"has builder fitted 15 or 22mm hot supply" Definitely 22.

"you cannot fit a pump or un-vented cylinder on this shower." Noted - the plan was always to replace the Trevi Boost with a normal mixer.

Thanks again to you all.