Hot water tank thermostat problem

we are having several issues with thermostats fitted to a hot water immersion tank. I would like help with the first before progressing to the 2nd which is thermostat for the oil burner.

When we switched the electric water heater on recently there was a bang and the fuse tripped out on the main board. We decided to replace the thermostat hoping to get that possible issue out of the way. we purchased and fitted a new thermostat and was pleased it started up straight away. After a few hours tho we had the water coming out scolding hot.

I read about altering the thermostat and turned the dial to here the click, the element stopped but then started again as soon as released the screwdriver. I repeated the turning and clicking to discover it went off completely before noticing it was depressed down and stuck, so could not come up. This kept the element off but as soon as I freed it the element came back on! 

so so now tried it again by turning the arrow and pressing slightly which gave the click before releasing and on it came again. I noticed every time I pressed the dial down it clicked off and as soon as releasing it clicked back on. So the removed the thermostat and put back in the old one, lo and behold same issue. 

can an someone help please before we go back to the plumb shop? Was the new one faulty? Is this issue a fairly normal one? I will be going into detail on my other thermostat which is oil fired rather than electric and try explain the issues there. currently we just seem to have a constant scolding hot water issue whether from oil fired or electric. I think they are two completely different issues but so annoying coming together. thanks for reading

Sounds like a faulty thermostat. The bit you turn should not "push down" it's purely a rotary dial that sets the switching temperature.

If you are talking of an oil fired boiler heating the same water tank, then you can't make any sense of whether the boiler is over heating the water until you sort out the immersion heater (or just turn it off, why do you need it if you are heating water with the boiler?)

Dave, 

Doesn't pushing down the rotary dial force the contact to open and close? I know it's not supposed to and they should be handled with care. No need for any pressure from a screwdriver. He's possibly a little heavy handed. 

He's probably brokern the new one.

Thanks guys for your answers, If heavy handed is the problem then hands up. Did not touch the dial from its factory setting until after it got scolding hot though. Then turned dial to lower the setting, but thanks will replace.

We do not use the electric immersion due to having oil boiler but have had lots issues and needed a quick fix hence turning the electric on, going bang, changing, very hot water etc etc.

The exterior thermostat for the oil fired boiler seems to be located near to the bottom of the tank. The fitter said the wireless was not working so put an electric cable through from the junction box to it. As we kept having issues with the hot water coming out too hot we decided to change the thermostat. in doing so we noticed although it was a 4 core cable only 2 were used the other 2 were cut one was grey the other earth. on tracing back to the control box we could see all 4 were wired in. So very unsure about why they had done this. does one cable not tell the boiler it is satisfied? recently the plumber fitted a new  pump but did notstayand hasn't been back yet. For some reason the pump stays on 24hrs a day even when all heating and water are timed off. We have had to isolate the boiler in middle of night due to it burning even though everything is off, this only happens when we use the hot tank in b&b bathroom. it seems the tank has been constantly calling for more heat even when all the timing gear is off! 

Appreciate your Time in reading and responding, many thanks

A 4 core cable to a thermostat is usually earth, neutral, live in, and switched live out.

The earth should be connected.

The neutral is often not connected for a tank thermostat as you are not bothered by a bit of hysteresis.  It is usually only used on a room thermostat where an accellerator heater overcomes the normal hysteresis of the 'stat.

The boiler and pump staying on is probably a motorised valve that has failed.  I suggest you get an electrician that understands heating controls to have a look at the whole system.

Geeeeez it sounds like your boilers wiring is a right mess..

I'd say that you need to get an electrician (NOT a plumber) in to check it all out and sort it out

Thanks guys, not just the wiring but the boiler and plumbing as well. local trades people around here not the most able but what it's what we have. we live in a beautiful part of the world have few people but do need to have a open mind. 

The heating engineer brought a local qualified large electrical team to do the electrics, and the oil fired system was done by himself a sole qualified trader. as a consumer we can only trust people know what they are doing and let them get on with it. After so many problems over the years since it was fitted I decided to investigate myself. The electric Thermostat is to get us through this problem, so will buy and fit another one.

The  thermostat on the hot water tank for the oiled fired boiler is placed very close to the bottom, is this correct? I have read a third up the tank is the best place. I am trying to take it all one step at a time so can eliminate the issues without having the major problems we have been having. We called the plumber in as central heating and hot water stopped working. he fitted a pump then left. Charged us call out £40 plus £40 per hour, which we accept but can't keep paying out hoping someone can fix a problem when there seems to be so much contributing to the big picture. 

Do appreciate your time in reading and responding, I am not qualified or an expert my dad was an electrician and have helped him wire up houses etc over the years, so am not bothered by my investigations as have a logical brain, the will get a qualified man in to do the work. many thanks

It sounds as though the 'electrician' has got his wires crossed in the electrical connection box for heating/hot water system. 

As for the immersion stat, as said there is normally a dial which you turn to alter temperature of output water, this dial should be numbered (usually in degree c), next I the dial there is usually a black cap with a screwdriver slot in it, this you unscrew to access the safety trip which is a push button to reset. 

As for the tank stat then usually they are fitted between 1/3 to 1/2 way up the tank. 

As my esteemed colleagues have suggested a good electrician with heating control knowledge is what would be required in this instance. 

Perhaps the next person you employ, you should make it clear the payment is based on results.

i.e. if it still doesn't work, no payment, or he comes back again for free.

I would never have the cheek to charge for "fixing" something when it is not fixed.

Thanks again everyone, its so refreshing to be able to ask questions and get several answers to work with. I have traced the wires from both tank thermostats back to the LWC 1 wiring centre. The wires in both thermostats were Brown to Com and Black with Brown sleeve to 1, so no surprises there.

However after going through the LWC 1 the wires go down cables to the Digistat, from tank 1 connections they use the Black with brown sleeve and for tank 2 they use a brown.

The black with brown sleeve from the digistat (tank 2) goes to the room stat (9) on the LWC 1. 

The brown from Digistat for (tank 1) goes to (11) which says L Programmer

Tmrw will check out where wires go to inside Digistat box, maybe electrician mixed up wires as Sharpend suggests, will keep writing the routes down.

Tried again tonight with Tank 2 on oil fired and the water was scolding after 11/4 hrs, thermostat did not close until timer clicked off and valve closed. The thermostat is nearly at bottom of tank and so intend to move up to half way tmrw to see what if any differences there are, if not it must be wiring! Time will tell, once again thanks for your thoughts, they are appreciated. 

Try also turning down the boiler's thermostat. There's no need for the water to be that hot (you must have radiators too hot to touch as well)

Roderick Smith said:

Thanks again everyone, its so refreshing to be able to ask questions and get several answers to work with. I have traced the wires from both tank thermostats back to the LWC 1 wiring centre. The wires in both thermostats were Brown to Com and Black with Brown sleeve to 1, so no surprises there.

However after going through the LWC 1 the wires go down cables to the Digistat, from tank 1 connections they use the Black with brown sleeve and for tank 2 they use a brown.

The black with brown sleeve from the digistat (tank 2) goes to the room stat (9) on the LWC 1. 

The brown from Digistat for (tank 1) goes to (11) which says L Programmer

Tmrw will check out where wires go to inside Digistat box, maybe electrician mixed up wires as Sharpend suggests, will keep writing the routes down.

Tried again tonight with Tank 2 on oil fired and the water was scolding after 11/4 hrs, thermostat did not close until timer clicked off and valve closed. The thermostat is nearly at bottom of tank and so intend to move up to half way tmrw to see what if any differences there are, if not it must be wiring! Time will tell, once again thanks for your thoughts, they are appreciated. 

Click to expand...

So are there two hot water cylinders? 

The cylinder thermostats shouldn't connect to a digistat (which is a Drayton branded wireless room thermostat (usually)) 

this is is going to almost impossible to fix without some pictures of all parts of the system and an accurate diagram of exactly how it is connected, along with confirmed tests of voltage being present or not at various stages in the control system under various switch positions.

Thanks again will post more info soon. lots problems with Internet just now! To add to our woes.

Turner down boiler thermostat today to min and adjusted radiators so nearest had thermostats set low, the far end of house has no thermostats due to constantly not working since it was put in. This did help lower water temperature in both tanks. I did notice today the thermostats on both tanks can turn on and off the valve at their lowest setting by hand, but water still too hot so need to limit time on. Tank 1 which is our room and kitchen also appears to then stop valve but even if set it to 50 the temperature of water is too hot for hand under tap. when turned up boiler temperature it did little for central heating but cooked the water in the tanks for hot water!

Going to to buy water and room thermostats to help but still feel something with wiring is wrong. As Dave says above should not be wired into wireless! But it is. Hopefully when finished will have lots info to help electrician do his job quickly. Once again many thanks.

These tanks what make are they? Are the stats the wrap around type (older method) or are they built into the tank itself? 

The valves will have a metal lever which allows you to turn them over by hand, this is for manual operation should all else fail. 

Ideally the stat should be operating the valves if all working correctly (although you would still be able to move the lever by hand it's not under any great pressure). 

Can you give a step by step breakdown as to what happens when you switch heating off and water on, then water off and heating on, and finally both on and both off. Sorry if you have given some detail already I just find it easier to diagnose when broken into simple steps. 

Will write up a detailed description for you tmrw. I need step by step clear info to help me work best so will try and write in as clear as can ways.

The tank thermostats are the ones that are held on by wire HTS3 from Drayton. we have guests into night so had to get water and room temps done ready but will have another go tmrw to record what happens when turned on etc. Would it be better with pictures and saved as PDFs? As writing here might take a long time! I really appreciate the time you guys spend helping others and can appreciate the need for clarity and detail so that is what will do.

It is clear from today our boiler is on the limit to heat this house, which is an old farmhouse we rent from the National Trust but is on a fully repairing lease so all our responsibility! When asked to heat most of the house with boiler full temp and pump full go it could not get end rooms up to temp. Got hot water tho very hot. we had old Stanley cooker before this linked to water and couple rads, just needed coal and it was great, this central heating was meant to be our way of preparing for the latter years, we are both in 60's! When we have enough information we are considering writing to the electricians who did all the wiring and asking if they would like to put it right, it's years later and the problems have covered up the mistakes made when installed, our hot water has never worked consistently correctly. Time to get to bottom of this has come, hopefully with your diagnosis I can find someone who can put it right, so many thanks.

It sounds like the system may be very poorly balanced. 

This is a side issue to the other problems you have, but every little helps.

there should be a manual valve on the return pipe from a high cylinder coil to allow the CH to be balanced against the DHW. Also proper balancing of all the radiators may be required to sort out the poor distribution of the heat around the system.

it may also be that the pump is inadequate or that the pipework is just full of gunk and needs to be powerflushed to clean it out and get it working properly. 

Also giving us a clue as to your location might help us with recommending someone local who knows what they are doing.

Thanks Dave we live just outside Minehead Nr Porlock. I have started to video today first with our tank which can be an issue but not like tank 2. I have purchased a water thermometer to get a better idea of tap temperatures. I will edit and post video tonight to start the process off, this evening I will then video the tank 2 reaction to temps etc. I appreciate and except this will take some time to get a better picture before someone comes in and repairs, hence the video so you guys can look at what happens over time etc when the water 1 is done separate, water 2 done separate, maybe both together, CH on its own and then all 3 together. 

When the CH engineer came out he often increased boiler temp to get CH hotter down the far end of the house, plus working pump on full speed, but thats when the water in tanks got too hot! Most of the radiator valves went in 1st year or so, a new motorised valve was replaced, the guy who came for that said we were lucky as he had one but they don't make them anymore. We used to have a huge air problem then one day I noticed a small stain on ceiling and realised it was under CH pipes. He said it was a joint he forgot to solder, guess one small mistake is acceptable. We have complaints about water temp from time to time and apologise but then for a while none, so we did not explore further, now its time we accepted the responsibility to get this sorted. 

Thanks for your time as the rest of the guys here, will post later

Roderick Smith said:

. 

When the CH engineer came out he often increased boiler temp to get CH hotter down the far end of the house, plus working pump on full speed, but thats when the water in tanks got too hot! Most of the radiator valves went in 1st year or so, a new motorised valve was replaced, the guy who came for that said we were lucky as he had one but they don't make them anymore. We used to have a huge air problem then one day I noticed a small stain on ceiling and realised it was under CH pipes. He said it was a joint he forgot to solder, guess one small mistake is acceptable. We have complaints about water temp from time to time and apologise but then for a while none, so we did not explore further, now its time we accepted the responsibility to get this sorted. 

Click to expand...

Ok there's no way he was an engineer! I'd say he was most likely a cowboy. 

Yep now would agree with you, local man who ended up in court for being 'feelie' with the ladies who were at home when he called! 

He did not do the wiring tho and I spent the afternoon video the sequence through to the wiring for the main water tank which is our and kitchen. All has gone well and the thermostat does appear to be working at cutting in/out as needed. I have tested the water at tap temperature and left it at 50c. The thermostat is set at just under 60 and the water from tap and shower with hot only is too hot to hold hand under so all good for tank 1. 

Then traced the wires into the digibox and was just a little surprised at what I found, 1st of all one cable comes in and has 3 core with each one going to a place, then there is a second cable coming in all wires apart from one is cut, the one is wired into a connector, with nothing wired into the other side! so it does nothing at all at the digistat end, dead end, end of the line, hidden from view. 

Therefore so far I am convinced the 2nd tank is not connected to the digistat as is tank one but do know it is connected to the valve as it can open and shut it, however I now believe the thermostat is not able to tell its at temperature so keeps going. In effect the thermostat acts as a switch only as you can switch on the valve and switch off the valve but so far nothing else! I am finishing off my 1st video tonight which is tank 1, probably boring for you guys now but was my process. Video 2 will be the wiring as clearly there are issues here, more to discover, wont need a tank 2 video as now know some of why it does not work! Big thanks all around