low pressure/cut-off after 2 mins >> been told to replace/upgrade entire system!

[timtam]

Have attached short video link to make explanation easier

View: https://www.youtube.com/watch?v=yzBcvJTr10I


646 sqft apartment
1 ensuite bathroom
1 large(r) bathroom
150L(ish) boiler/water tank
Grundfos Amazon STP-2.0 B ( AP030) (i think)


00:00 Water pressure upon opening is fine with hot water all good
01:12 You can hear the water pressure slowly dropping
01:20 Water pressure just dies
[switch off shower] [you can hear water refilling up the tank]
03:00 Switch back on and it resumes
04:40 Pressure starts to die again.


The ensuite bathroom next door runs on an electric shower unit - and strangely doesn't seem to have problems (as far as i can tell)

Water is most definitely not running out after 1min30secs - although it sounds as if the pump is sucking/drawing on air.
Having difficulty identifying what exactly is the source of the problem.

Also note - in the kitchen next door when the tap is turned on, there is a slight pause, you can hear the motor kick in before the water flows (not sure if that helps)
Had one plumber come in who immediately suggested replacing everything with a Gledhill PulsaCoil Eco Thermal Store PCS180ECO (around £880) plus labour (around £400)

I know that these Gledhill models are great, but this is not a +£1k problem in my opinion!

Looking instead to replace/upgrade with a Gledhill Stainless Lite Plus Open Vented Direct Cylinder 150L at a more reasonable £350, which apparently is mains-pressure driven (which may dispense the use of the existing pump?)


Any thoughts/opinions would be greatly appreciated!!

 

[steadyon]

1. If your cold water storage cistern (CWSC) is the small tank above your hot water cylinder, then my guess is that the cold water supply is running out very quickly, causing the pump to stop. There is no simple answer to this unless you have the space to install a larger CWSC.
2. To install an unvented cylinder, you must have:
2a. Decent pressure from the incoming cold water main. Absolute minimum of 1.0 bar, preferably 3.0 bar (dynamic pressure). If you want to run both bathrooms of an unvented cylinder, the incoming mains within the house would need to be 22 mm, coming off a 25 mm feed from the water board.
2b. Decent flow rate. Minimum of 20 litres per minute, best at around 30 to 35 lpm.
2c. A means of getting pressure relief pipework to outside and correctly terminated.
2d. The installation must be notified to your local building control office. The installation MUST be by someone with a current G3 qualification, and that person will normally notify building control.
3. Don't know about Gledhill, but most unvented cylinders come in two forms, the bare cylinder, or an installable system with all valves and controls. If your estimate of £350 is correct (which I doubt), I would expect you to have to pay around another £200 for the necessary controls.
4. Installation cost will primarily depend on the amount of work required to get an acceptable incoming pipe size connected, and the the amount of work required to route the pressure relief pipework. Don't know where you are based, but in outer London I doubt it would be much less than £800.

 

[SimonG]

Not enough stored water. Doesn't matter how big the cylinder is, it's the cold water storage tank that determines length of shower.

But just over 1 minute is quick.

Have you checked water level in cold tank? May need float valve adjusting.

Wouldn't be fitting a thermal store unless you have multiple heat inputs..

As said above pressures and flow need to be checked. Static pressure, dynamic pressure (with a tap open) and litres per minute flow on your mains cold water.

 

[timtam]

1. If your cold water storage cistern (CWSC) is the small tank above your hot water cylinder, then my guess is that the cold water supply is running out very quickly, causing the pump to stop. There is no simple answer to this unless you have the space to install a larger CWSC.
2. To install an unvented cylinder, you must have:
2a. Decent pressure from the incoming cold water main. Absolute minimum of 1.0 bar, preferably 3.0 bar (dynamic pressure). If you want to run both bathrooms of an unvented cylinder, the incoming mains within the house would need to be 22 mm, coming off a 25 mm feed from the water board.
2b. Decent flow rate. Minimum of 20 litres per minute, best at around 30 to 35 lpm.
2c. A means of getting pressure relief pipework to outside and correctly terminated.
2d. The installation must be notified to your local building control office. The installation MUST be by someone with a current G3 qualification, and that person will normally notify building control.
3. Don't know about Gledhill, but most unvented cylinders come in two forms, the bare cylinder, or an installable system with all valves and controls. If your estimate of £350 is correct (which I doubt), I would expect you to have to pay around another £200 for the necessary controls.
4. Installation cost will primarily depend on the amount of work required to get an acceptable incoming pipe size connected, and the the amount of work required to route the pressure relief pipework. Don't know where you are based, but in outer London I doubt it would be much less than £800.

Not enough stored water. Doesn't matter how big the cylinder is, it's the cold water storage tank that determines length of shower.

But just over 1 minute is quick.

Have you checked water level in cold tank? May need float valve adjusting.

Wouldn't be fitting a thermal store unless you have multiple heat inputs..

As said above pressures and flow need to be checked. Static pressure, dynamic pressure (with a tap open) and litres per minute flow on your mains cold water.

Hey @steadyon / @SimonG

Thanks for the response and detailed analysis.

TBH - wasn't expecting much activity during the festive season!

Yes you are correct - general consensus has been that the cold water tank above is too small - so an increased-size cold water storage cistern is a must.

I've had a couple of contractors come in each with different quotes, varying from 1200 - 2500 all in - but for thermal storage heaters/boilers

They (obviously?) don't seem to want to quote work for installing the other cylinder i was looking at:

Gledhill Stainless Lite Plus Open Vented Direct Cylinder 180 LitrePLUDR180OV which is around the £350 mark.

I'm being 'cheap' purely because this is a rental property. I have no problem spending more if i was residing at the property for sure.


Going to get a couple more opinions before deciding.

THanks and have a merry Xmas and Happy New Year!

 

[centralheatking]

I dont like Gledhill stuff, seen way to many go lala in McCarthy Stone apartments, they make a whole business from repairing their inadequate products ...centralheatking

 

[steadyon]

For what its worth I agree with centralheatking re. Gledhill products. Overpriced spares and very poor service in my experience.

 

[timtam]

Wow - ok - seems like nobody here is a fan of Gledhill! 🤣

Honestly - i only know by what is recommended to me.
On paper (ie internet) the specs for what has been recommended:

PulsaCoil ECO Stainless <link>

But since starting this online post/enquiry - anytime i mention Gledhill - the brand/products have been slated!

I may just go down the route of increasing the size of the water tank for now as a temporary quick-fix whilst planning a more robust solution somewhere in the not-too distant future....