New Unvented Cylinder flow rates and temp fluctuations?

we have had a Gledhill 300litre unvented Cylinder installed by a G3 installer

The problem is when we are in the shower and if someone opens another tap or flushes the toilet the temperature changes in the shower which is dangerous for the kids and adults - is this because it’s not a thermostatic shower? Although we never had a problem with this shower when it was vented system with a pump?

However the biggest problem we are finding is for example if we run the hot water to fill the bath the other outlets for hot nothing comes out - so if someone is in the bathroom then they can’t wash their hands if the bath is filling?

The Gledhill docs says it needs 3bar pressure to operate but our installer said that our 2bar pressure (he said it was 2.5 bar at non peak times) would be good enough and our flow rate is 14litres

We had a new water main fitted 3 years ago (blue pipe 22mm?) and enters the house under the kitchen sink via an insuduct blue plastic pipe but straight after the stopcock it goes into 15mm copper and is rerouted around the house until I suppose it reaches the room where the cylinder is - is the 15mm what the problem is?

Should we extend and move the water main the 3 metres so it starts in the utility area and a 22mm feed can go into the Gledhill cylinder

With your new system, every outlet (hot or cold) is sharing the direct supply from the mains. A thermostatic shower would certainly help with temperature fluctuations but your main problem is the mains flow rate. 14 lpm at 2 bar is not great. Where was this measured? A 300 litre cylinder should have a 22mm supply so upgrading this may help. I assume you've done the obvious things like checking all stop valves are fully open.

20 lpm is usually considered the minimum flow rate. Was the flow rate measured at the stop cock? If it was significantly more, you should definitely have 22mm pipework to the cylinder. You should also have as much 22mm to your outlets as possible, especially to your shower.

Thanks all for your replies, really appreciate it.

I think they measured it at the outside tap near to where the cylinder was going to be located.

The 25mm blue main comes in and at the stop cock goes straight into 15mm copper, it then goes quite a convoluted way before the pipework ends up by where the tap they measured the flow rate. Anyway the tap has now gone and this 15mm copper then goes into the PRV and it is a 22mm pipe into the cylinder

If you was in my position what would be your next steps, asking the installer to come back to rectify? After all if you are running a bath and you cant get hardly any water out of other upstairs outlets or even to refill the toilet to flush then this is not ideal!

It depends on what the installer was hired to do. If you asked him to install the best system for your property, he has clearly failed. If you asked him to install an unvented cylinder because you'd heard it was the best, he's done what you asked.

I would suggest though that if you have a new 25mm MDPE main and 2 bar at the property boundary, then there should be a sufficient supply if you get the internal plumbing sorted.

You'll need to plumb in a few gauges to determine where the problems are...I suggest for a start a gauge connected just before the cylinder pressure reducing valve.

I am not familiar with the Gledhill, however some cylinders have a pressure balancing valve at the cylinder with all the cold outlets taken off this. So that means at least a 22mm pipe has to be taken from the stop cock to the cylinder. Irrespective, 15mm is way too small. The cylinder needs a dedicated 22 pipe to it from the stopcock. Also, a full bore stopcock should be fitted, but the Insuduct usually comes with its own stopcock.

Agree with Elkato - if your installer has installed the system you asked for, then he has discharged his duty and can't be expected to "rectify" anything. It's not his fault your mains supply is crap, and you can't get out more than you put in.

I'd remove your Insuduct temporarily, cut into your incoming main, and test the available flow rate there. That'll give you a true reading so you'll know for certain what you have available to work with before you rip your house apart extending 22mm to your cylinder cupboard. If you've only got 14l/min coming in, that's all you're going to get out unless you have space for an accumulator

For starters yes, I would say as a minimum you need to look at getting an unrestricted 22mm supply to the unvented cylinder.

At the cylinder, there should be a pressure reducing valve/saftey group valve set, which the 22mm cold supply enters, from there, its should split so that you have a 22mm cold feed into bottom of cylinder, and a 22mm cold "balanced" supply going to any mixer taps/showers that you have (or simply to all the cold outlets) this way the pressure of water feeding into the hot and cold taps are about the same allowing them to mix correctly, and not have a lower pressure to hot than cold.

Once those are done correctly I expect it would be better, but may not be quite as good as your previous set up, if the gledhill doc says 3 bar minimum, then really your expectations need to be realistic if you dont have that.