Hot water tank thermostat problem

[Davethsparky]

So does the cylinder 1 stat only operate the valve and have no effect on the boiler? 

That sounds reminiscent of a bodge method of adding temp control to a gravity system

 

[Roderick Smith]

Cylinder 1 stat is wired to control box and then one wire to valve and the other to digibox, when turned on past minimum it clicks and turns on the valve and will regulate the water to approx what the thermostat asks for, so as I increased it the water temperature went up. So now very happy Cylinder 1 is fine. In doing this found cylinder 2 is not connected via Digibox but is connected to valve as traced back the wires. Will trace the 'new' wire from the centre box and see where it goes. I have now moved both cylinder stats off min and turned on valves and moved back to min and turned off both stats separately so know they are at least doing one half of the job. As cylinder 1 works ok can only assume the wiring into digibox is correct and this is how thermostat turns off the valve, as Cylinder 2 is not connected to digibox presume it cant shut when reaches temperature which is why it just gets hotter and hotter.

This link is to video about cylinder 1 which shows all the components from boiler through to electric boxes etc, but it is just about setting temperature and checking the thermostat is working correctly. I have learnt so much feel ready tmrw to video the wiring through from cylinders to ? then hopefully you will have a better picture , of the problem. Maybe watch the beginning for all the components to have an overview then video 2 will be the detail. Thanks

 

[Roderick Smith]

Ok here is the wiring tracing video, I have followed the wiring for Cylinder stat 1 first as this stat is working well. One goes to valve the other to digistat.

The other cable coming into digistat box is worrying, its a 3 core with 2 wires cut out and the brown put into a connector which is live but appears to do nothing.

Following wires for Cylinder stat 2 discovered one wire goes to a valve same as wire in C1 does, however the other wire goes to the programmer timer and not the digistat as does C1, so here is the problem I thinks, I will leave it to others for their opinion.

 

[Sharpend]

From what I have seen and I haven't time to watch it all. 

The first video would suggest that this is working as it should be. Slight temp changes could be subject to heat loss in pipes, distance of transfer to tap etc. 

The second descriptive you give doesn't quite seem right. It would not be necessary for the cylinder stat to be connected to the digistat? The digistat is for the heating? 

Yoy are looking for a connection from programmer/time switch to a stat (be it cylinder or digistat) then to the relevant valve. 

If you are correct in that two stats are linked then this would suggest that one cylinder is being heated both when the cylinder calls for heat and when the digistat operates? 

Can you try to turn heating only on and see what valves operate? 

 

[Roderick Smith]

Thanks Sharpened the 1st Cylinder does appear to be working correctly and is wired through the Digistat which right or wrong is working correctly as Temp in taps etc is holding at 50c. 

The Digistat is a wireless control for the heating Yes, but for some reason the electricians who are a company that also do plumbing wired it through the digistat, as said above whether rightly or wrongly it does work.

The 2nd Cylinder thermostat does not work on the temperature control though and in tracing the wires can see it does not pass through the digistat as per Cylinder1. Instead the wire goes up to the Timer box. (Indicating to me it is wired to come/go off with the timer)

With both C1 and C2 a wire goes to their respective valves and works them correctly, so the problem is getting the thermostat on 2 to work like 1 does. The 2 stats are not linked together as they work 2 different Valves, apologise if have confused you with my description.

There is three timing channels that work three valves, Heating for the Heating, Heating 2 which is the C2 and Water which is C1. Heating and water both work correctly in turning on and off with the timing and the thermostats. C2 comes on with the timing and goes off with the timing but the thermostat does not function at all.

My reasoning is that if C1 works why did they not do the same with C2? I do not know or understand the correct way to wire etc but do know C1 works as video 1 shows. 

 

[Roderick Smith]

Thanks again Sharpend for your questioning, re traced my steps and made one huge mistake in tracing a cable so going to go back through again. The cable does not go to Digistat so my mistake there, they both go up to Timer, so now very confused and will re do my tracing!  :Blushing

 

[Sharpend]

do you have a multimeter you can test with? 

 

[Sharpend]

From your first video- does the second cylinder operate the same way?, if so this would suggest that this is also wired correctly. If not then there is either a faulty item or incorrectly wired. 

 

[Roderick Smith]

I will test the Cylinder 2 and stat same as did 1 to prove what happens, so can provide more detail.

Sorry got knickers in twist on tracing wiring etc and wanted to show what found. Have re done but from different angle so have roughly drawn out the wiring back from the Timing unit. There are 2 large white cables that come into wiring centre from the Timer and have followed them to ends. Hopefully my diagram works.

 

[Roderick Smith]

Big apologies for getting my wires crossed! got hung up on the Digistat after tracing a cable through, so re started whole process again, fair play to you guys for keeping a clear mind whilst problem solving as it is not easy.

I have turned down the boiler temperature as suggested and it is currently working at a 1/4 on, does not give degrees or numbers just a line getting bigger!

I turned the pump down to medium to then set the central heating and water.

So Cylinder 1 test showed the water temperature at tap is a fairly constant 50C using the Drayton HTS3 thermostat.

With Cylinder 2 found the water was still coming out too hot and with the pump the shower was impossible, I swopped the thermostat over with Cylinder 1 as knew this one worked ok. The Valve actually turned off but with water too hot so turned thermostat down to its absolute minimum and still too hot.

Decided to buy another make of thermostat as was using 2 Drayton HTS3's, and bought a Center thermostat which has done the job! Have set it to minimum which is 40C and water out of the tap is 50C! so big relief there. Clearly better at the lower end! Not sure why we have such differences but it's what I have found in this case.

Now learning to balance radiators so have a more uniformed heat over the house, what is showing up which is how I believe we got into this mess in the first place, was in order to get more heat people turned up boiler and increased the pump to max, (probably why last pump stopped working!) The end bedroom which we use as b&b is very large and the radiator on full bore is not getting room temp above 17C, so my thinking is as we have one in hall we never use I am going to get plumber/heating engineer to take it out and put it in bedroom then can reduce lockshield down to suit, I think this will mean we can run the whole system at a lower temperature at boiler and maybe turn down to min setting on pump. This hopefully gives us leeway for when it gets colder!

I have discovered about a thermostatic mixing valve to correct the hot tap water temperature, to safeguard b&b guests I think we should get plumber to fit one for safety reasons. Any thoughts?

You have all been a huge help, a big thanks to all and if any of you are ever down this way look us up at Exmoor Owls and come fly a bird as my treat. In meantime know you being at end of the internet is a huge help especially to old buggers like me who cross their wires. 

 

[Sharpend]

So a thought on hot water temp variance. If the stat is fitted too low on tank then physics means heat rises, thus waters higher up the tank will be slightly hotter than the lower of the tank. May try moving stat? 

Blending/mixing valves are all the rage at the moment a regulation requirement I believe so good idea to add one in for guest area at least. 

To balance the radiators, the nearer the boiler the lower the lock shield should be tightened down restricts flow through thus allowing it to carry through pipe work to other radiators. 

 

[Rob_the_rich]

50 deg C in the cylinder might not be enough to kill off legionella, 60 is what it is normally set at.

Thermostatic mixing valve for taps is  good way of ensuring safe water temps, you might want to put a thermostatic shower mixer in too

 

[NozSpark]

Here's some info from the WHO..
 

I thought that stored water should be heated to 65deg

Above 70 °C (158 °F) – Legionella dies almost instantly

At 60 °C (140 °F) – 90% die in 2 minutes (Decimal reduction time (D) = 2 minutes)

At 50 °C (122 °F) – 90% die in 80–124 minutes, depending on strain (Decimal reduction time (D) = 80–124 minutes)

48 to 50 °C (118 to 122 °F) – can survive but do not multiply

32 to 42 °C (90 to 108 °F) – ideal growth range

25 to 45 °C (77 to 113 °F) – growth range

Below 20 °C (68 °F) – can survive, even below freezing, but are dormant

 

[Rob_the_rich]

Here's some info from the WHO..
 

I thought that stored water should be heated to 65deg

HSE says 60 or above http://www.hse.gov.uk/healthservices/legionella.htm so 65 seems good. LFB might have something to say on the matter though.

 

[Roderick Smith]

Thanks guys, should have mentioned on Cylinder 2 (problem one) I moved the Thermostat up from the bottom to just about half way, which is what started the changing stats thinking. They had fitted original thermostat opposite where the cold comes into the cylinder, so you probably can guess what temp it was always recording the tank at and constantly asking for heat to warm up the cold water!

Going to check these blending mixing valves out and like the idea of a shower one as we have two guest shower rooms that need to be safe. Hopefully the extra rad will also ensure more comfort and less hard work for boiler and pump! Once again many thanks :signthankspin: