Thermostatic Shower Issue with Cold Water Overpowering the Hot?

[Madrab]

That's not an anti gravity loop, nor is it taking the feed from a flange.

That's just a downwards facing feed from the normal vented HW supply, it's been tee'd like that to reduce the amount of air that could be drawn into the feed to the pump, rather than a flange being fitted to the cylinder but I'm afraid to say that simply hasn't been installed properly at all and certainly not in line with the MI. Not surprising that it's struggling.

The NRV, in the salamander diagram (just above the H outlet on the pump) is to stop HW backflow and being syphoned/drawn back down into the cylinder creating negative pressure in the pipework. It wouldn't be fitted to increase the flow through the hot outlet I don't think ... @just pumps?

The only reason I can think why there is an imbalance that is corrected by drawing extra cold water is that there is a higher cold water flow than hot that is then balanced out by drawing more cold from the pipe supplying the pump.

The pump should have its own dedicated supplies from both the HW cylinder (flange) and the cold water cistern (separate feed), that doesn't seem to be the case at the moment.

 

[Alfie_Huntingdon]

Thank you @Madrab.

I see what you mean about not having a dedicated feed for the pump, although all upstairs hot water taps, showers etc are fed by the pump and only two downstairs taps are fed outside of that loop and are never on at the same time as the shower so I'm not sure why that could cause a loss of flow.

The cold side of the pump is fed by a dedicated supply from the cold water tank and is gravity assisted. I would have thought the thermostatic valves within the showers should be able to deal with at least a small imbalance between the hot and cold flows.

It seems like my plan of attack is to first fit the non-return valve as a cost-effective solution before either getting a plumber out to create a dedicated connection to the hot water tank or trying new shower valves.

I'll report back!

 

[Madrab]

Unfortunately it's really difficult to give specific advice not being onsite to see the orientation of everything in relation to each other. Where is the cold water cistern in relation to the pump? it almost looks as the feeds are inverted too? In other words the feeds are rising up above the pump in relation to the cold water cistern and the cylinder.

I must be honest though and you won't want to hear this, with the issues/mistakes seen up to now, I'd be looking to take the installation back to the start.

 

[Alfie_Huntingdon]

Hi All

So I had a bit of a play around yesterday and fitted the non-return valve on the hot side immediately after the pump.

Unfortunately, that made no difference to the shower performance.

I then thought I'd try and partially close the isolating valve on the cold side to see if this would address the imbalance. Even with the cold running with a low flow (confirmed by running a cold tap) the shower would still not heat up properly unless a cold tap was also running. It seems almost any supply of cold water is enough to overwhelm the hot side.

So unless I am missing something really obvious, I'm really struggling to work out what is going on here and it is making me think it is more of an issue with the showers rather than the pump/pipework.

Any further thoughts would be very welcome!!