Hot water cylinder too hot

[Djlm12]

Really appreciate all your help. I know it can be frustrating talking to us newbs!

 

[stem]

Now to the cylinder stat. If I have BOTH heating and hot water on (middle position of the three way port) changing the stat does not effect the position it stays central and continues heating both.

That's a classic sign of the missing wire I mentioned, the one that tells the MV to close off the HW port. But it could also be caused the stat being faulty and not making the wire live, or the valve itself.

If I have just the hot water on (in water position of three way port) changing the stat does not move the position or stop the flow or turn the boiler off. (So that leave the issue being with the stat or wiring?).

As I said the valve at rest sits in HW only position, so that's OK. However, changing the cylinder thermostat when only the hot water is on should stop the boiler.

With the heating and hot water both 'on' and calling for heat such that the valve is in the centre position CH & HW. Does it move to CH only when you turn off the hot water at the Nest?

And as @JohnD says "it's not fine" the valve shouldn't be 'letting by' whatever setting the pump is on.

From what you say, you may have more than one fault.

 

[JohnD]

If it was me then (as well as ordering a new 3-port valve) I would be probing the connections with a multimeter to verify they are correct and receiving/sending the right signals. But if you are not used to this work it can be dangerous, and you might accidentally touch a metal pipe at the same time as a live wire.

I find it much easier if you have a "wiring centre"

 

[Djlm12]

I definitely think I have more than one issue but thankfully I think you guys are helping me figure it out. So thank you

That's a classic sign of the missing wire I mentioned, the one that tells the MV to close off the HW port. But it could also be caused the stat being faulty and not making the wire live.

At this point would it harm to replace the cylinder stat and ill know for sure its not that?

As I said the valve at rest sits in HW only position

Im 99% sure that if I have heating on only and then it shuts off that the valve stays in the heating position. So im going with this is also an issue.

With the heating and hot water both 'on' and calling for heat such that the valve is in the centre position CH & HW. Does it move to HW only when you turn off the hot water at the Nest?

Do you mean something else here?

And as @JohnD says "it's not fine" the valve shouldn't be 'letting by' whatever setting the pump is on.

Understood that this is deffo a problem.




I think I have two issues. A faulty stat not reading correctly and also a faulty three way valve that doesnt shut properly and lets water by. Both in my mind need replacing.

 

[stem]

I don't think you fully understand how the 3-port valve works. There's a good explanation here.

Ideally you need someone competent with a multimeter who can make tests safely and check that the right wires at the MV are being made live when they should be. If they are, and the valve's not performing as it should then a new MV is the way to go, if the wires are not providing the right signals, there's another issue.

 

[ianmcd]

Is it something simple like you have a back up immersion heater that has been turned on accidently ?

If the pump is the only item in the loop that tells the Boiler to come on or off.

The pump doesnt tell anything to come on or off, the 3 port valve tells the boiler and pump when to come on or off

 

[Djlm12]

Is it something simple like you have a back up immersion heater that has been turned on accidently ?

The pump doesnt tell anything to come on or off, the 3 port valve tells the boiler and pump when to come on or off

Sorry that was a miss type I understand thats not the case now. No the immersion is not on to the best of my knowledge

 

[Djlm12]

I don't think you fully understand how the 3-port valve works. There's a good explanation here.

Ideally you need someone competent with a multimeter who can make tests safely and check that the right wires at the MV are being made live when they should be. If they are, and the valve's not performing as it should then a new MV is the way to go, if the wires are not providing the right signals, there's another issue.

Thanks for your help.

I am fairly handy with a multimeter.

When I get back later I am going to do the following things:

1. Check the wiring as per the diagram originally posted in case of an obvious issue.
2. Manually check the valve see if it turns freely as suggested
3. Check connections with a multimeter

I have always suspected and now you guys have confirmed the 3 way port has had a fault with the water being bypassed so I will look at getting that changed asap as regardless of the other issues that shouldnt do it.


I will report back my findings tonight.

 

[Djlm12]

I think posting an outsiders link broke my reply to you @stem


Thanks for your help.

I am fairly handy with a multimeter.

When I get back later I am going to do the following things:

1. Check the wiring as per the diagram originally posted in case of an obvious issue.
2. Manually check the valve see if it turns freely as suggested
3. Check connections with a multimeter

I have always suspected and now you guys have confirmed the 3 way port has had a fault with the water being bypassed so I will look at getting that changed asap as regardless of the other issues that shouldnt do it.


I will report back my findings tonight.

 

[ianmcd]

If you turn the thermostat on your boiler to 60 degrees the water in the cylinder cant get any hotter than that until you work out whats wrong, definately check the immersion though, you would be surprised how many I see where they are adamant it is not switched on and it actually is

 

[Djlm12]

If you turn the thermostat on your boiler to 60 degrees the water in the cylinder cant get any hotter than that until you work out whats wrong, definately check the immersion though, you would be surprised how many I see where they are adamant it is not switched on and it actually is

Hi Ian, thank you ill do that.

Wouldnt the immersion be on 24/7 though? Its got a direct switch next to the tank which is off but I will remove the fuse to be sure thanks for the suggestion.

 

[ianmcd]

Hi Ian, thank you ill do that.

Wouldnt the immersion be on 24/7 though? Its got a direct switch next to the tank which is off but I will remove the fuse to be sure thanks for the suggestion.

The immmersion has a thermostat if it is switched on untill the water reaches the temperature that the thermostat is set to, then it switches off, but to be honest most immersion thermostats are cheap rubbish and fail often

 

[Djlm12]

The immmersion has a thermostat if it is switched on untill the water reaches the temperature that the thermostat is set to, then it switches off, but to be honest most immersion thermostats are cheap rubbish and fail often

Im counting down the hours till I can go home and play with it all lol. The whole lot is very old (excluding the very new boiler).

 

[Djlm12]

Quick update.

Changed the cylinder thermostat for a new one £15 from toolstation on way home. Boiler now turns off with stat controls instantly so thats one problem fixed.

Just the three port valve to swap at some point to fix the water pass by thanks guys