SOLVED. What position should gate valve be open on hot water tank?

ninjaef

In our airing cupboard we have a hot water tank. It's modern, got that thick dense foam factory fitted casing around it,  10yrs old,  The water *was* very hot and cosy (shower/bath). The hot water is unvented indirect system with mains direct cold water feed. So an exchanger built into the tank. The model is Santon Premier Plus PP150B (150 Litre Capacity).

My grandkids have got in the airing cupboard and turned the red wheel gate valve on the exchange heater -bless em , RRRRR.
Anyway, now the hot water isnt as hot as it used to be, nowhere near hot, and it used to stay warm for 2 to 3 days but now its back to cold in 24hrs. So they have adjusted the wheel and upset the balancing. Need help! I have been on various heating sites and received conflicting advice. Have we a central heating decent DIYer here or better, an expert. Some suggestions I have received are:

• Turn the gate valve fully open (anti clockwise) as it should be open. I did this and it was a little worse but still way off what it should be.
• Close it fully then open it a quarter of a turn. Did it, same, it was a little worse but still way off what it should be.
• Open it about half way. Did this and it wasn't worse but wasn't better either.

There's obviously a "sweet spot" probably related to the water flow speed/throughput. Too much and the water rushes through the exchanger too quickly, so the exchanger is not hot enough and does not heat the water. Too little and the return flow is blocked too much so the hot water cannot get into the exchanger, so the water is not heated.
Is there any way I can somehow get this returned to normal. I have asked a gas engineer - just phoned up on spec - and he quoted £250 inc callout + parts + VAT. WOW!!!! Help MSE !
I have a heat gun that is quite accurate and I can point it at the feed and return pipes and get a temp - so maybe there should be a temp drop across the two that I can find turning this wheel one way or the other , half turns ?? If so , what's the temp diff across the exchange supposed to be?

p.s. we've since put a lock on the airing cupboard!

grumbler

ninjaef said:

...Too much and the water rushes through the exchanger too quickly, so the exchanger is not hot enough and does not heat the water.

I don't get this. The exchanger heats water in the tank. The faster the water flows, the hotter the coil is and the faster it heats water in the cylinder.

ninjaef

Hi pal.
Really? 
I thought the gate valve restricts flow such that the exchanger is "energised" from hot water. There is a flow rate measurement to be set , in the installation manual , that says the pressure difference between feed and return must be 0.1bar. So this to me is consistent with some of the feedback I have received that the valve needs to be slightly restricting the flow out of the tank - by 0.1bar , whatever and however one measure that , I can't. 
As I say, I do have the capability to measure a temp drop across the coil feed/return.
Wiered.

ninjaef

Update @grumbler

Just been sent a text by a DIY friend who says:-
It is a balance valve I think , to  balance CH and HW flow. So it has no effect on how quickly the coil can transfer heat to the cold water it will depend on the temperature of the feed which will differ depending on flow (whether the balance valve is fully open or closed) Open and the HW (tank and coil)  "scavenges" the CH hot water destined to the rads. Close it and the rads get all the flow (and by definition the heat). But it is not as simple as "open it half way" - depends on tank, pipes, boiler, coil rating and much more.

Does this sound sensible? or...?

grumbler

This does make sense. Similar to a lockshield valve in a radiator.

ninjaef

Ok bud. Thank you.

Jeepers_Creepers

A photo would really help.

Gate valves are often used where a crude by-pass is required by the boiler, in which case opening it up means the hot flow ends up back at the boiler without doing its heating bit first. I'm not saying that's what you have as I simply don't know.

Photo please, plus make and model of boiler.

southcoastrgi

Pics pics pics 

grumbler

Jeepers_Creepers said:

Photo please, plus make and model of boiler.

See above

southcoastrgi said:

Pics pics pics 

https://www.advancedwater.co.uk/STOMEMO/A540-088-1501/Santon Premier Plus Sales Brochure.pdf

Jeepers_Creepers

Until Ninja comes back we are left speculating. Given that he's seemingly tried the gate valve towards both extremes and nothing much changed, I wonder if the little fingers could also have touched the cylinder 'stat - is it accessible of these models?

ninjaef

H folks.
Sorry for delay - been doing the usual weekender things. 
ALL the heating and hot water issues have been resolved. The answer - in this home, with this system, the commissioning of the system, the answer is to open all lockshield valves and the balance valve. This goes against information I had from "expert HVAC engineers" over recent days - and other people on forums too. Anyway, all done and I can confirm all issues resolved. The house now takes around 50 minutes to warm from 14C to 19.5C in the morning. It's been taking around 2.5 hours. The water is now so hot the showers need to be put on setting 3 out of 6 - they used to be wacked up to 6.

My DIY heating guy in London was right. He said not all systems are the same and there are so many variables at play - it took him several days to investigate and come back to me with the right settings which he said might well be "wrong" for another home.

Anyway, all done. @grumbler was right all along. 

EDIT1: Sorry, for those wondering: The tank is a Santon Premier 150B and the system is Unvented Indirect heating (no immersion heater - well there is but it's disabled from new when we bought the house). Sorry, no pics and there's little point now as it's all working. But you can google the above. Like I say, it is all working *fine* and *perfect*. 
I also was turning the wrong valve, it was on the CH not HW. They both look the same.

EDIT2: A feature in the problem, was the lockshields on the rads were almost closed (some friend of a friend came round about a year ago to "balance" the system - but my London contact said that's nonsense because this system doesnt need balancing as the rads and setup matches the "BTU" requirements of the house so all rooms will heat at the same rate - which is indeed what happens, now.
SOLVED

EDIT3: 
I felt I was being ungrateful to some of the forumites here who have helped me, and those who asked for pics, so, I found one and here it is, the two balancing valves circled in purple. Also shown is one of my empty demijohns for la vino