Another nest query

[Ohinever]

Thank you gentlemen for allowing me to query your expertise.

Equipment: grant 50/70 boiler was attached to a horstmann h21xl switch. No room thermostat. Timed on/off. Could only have heating on with water on.

Moved in six months ago and thought I'd update to a smart thermometer, because I'm a bit of a geek and like new shiny things, if if they aren't particularly useful.

So, swapped the horstmann over for a nest 3rd gen today. Used the old wiring diagram and the nest instructions to try to do the job.

Only didn't go to well. Strangely the central heating side now appears to be working independently to the water heating side. But the water heater does not work:the boiler does not fire up.

I appear to have pumps for both sides of the system. There is an immersion heater upstairs, with a thermostat. This seems to feed into the wiring from the water side pump (please see photo). The yellow wire from the immersion thermostat is it seems attached to the brown wire from the water pump. The red wire from upstairs is then fed into 6, call for hot water.

Forgive the state of the wiring-this off course will be tidied up once the system appears to be working properly.

Can anyone give me advice as to why my water heating system is not working. I also presume I have to remove in any case this immersion heater thermostat?

Many thanks in advance.

 

[stem]

Sorry, but from your comments, it appears you haven't got a clue what you are doing. You really need to get a professional in.

First of all, an immersion heater has nothing to do with the boiler. It is a totally separate item that heats up the hot water cylinder (generally as a back up in the case of failure of the main heating system) electrically using a 3Kw (13A) electric heating element. It should never be wired to a Nest. The Nest is designed to handle a maximum of 3A. If you were to put 13A through it you will damage it.

Also. If previously, you could only have the heating 'on' when the hot water was also 'on', that suggests that your plumbing system is quite old and is not presently capable of providing separate hot water and heating control. This is not strange at all, but perfectly normal for old installations. If this is the case, the system will need upgrading first before you can fit controls that will give independent heating and hot water control.

The Nest is really designed for heating systems with motorised valves (you don't mention any, so I assume you don't have them) that can control of the water flow to the heating and hot water, as well as having internal microswitches that allow both to control the boiler independently. Pumps on their own do not have that facility.

 

[Ohinever]

Sorry, but from your comments, it appears you haven't got a clue what you are doing. You really need to get a professional in.

First of all, an immersion heater has nothing to do with the boiler. It is a totally separate item that heats up the hot water cylinder (generally as a back up in the case of failure of the main heating system) electrically using a 3Kw (13A) electric heating element. It should never be wired to a Nest. The Nest is designed to handle a maximum of 3A. If you were to put 13A through it you will damage it.

Also. If previously, you could only have the heating 'on' when the hot water was also 'on', that suggests that your plumbing system is quite old and is not presently capable of providing separate hot water and heating control. This is not strange at all, but perfectly normal for old installations. If this is the case, the system will need upgrading first before you can fit controls that will give independent heating and hot water control.

The Nest is really designed for heating systems with motorised valves (you don't mention any, so I assume you don't have them) that can control of the water flow to the heating and hot water, as well as having internal microswitches that allow both to control the boiler independently. Pumps on their own do not have that facility.

Thanks for your reply.

Yes I appreciate that the immersion heater can be heated separately from the boiler. I was just mentioning that there is a thermostat on the water tank that appears to be wired into the water grundfos. I was suspecting that this link would need to be removed.

I have wired up a few switches in the past, with good effect, so don't think I'm totally clueless. As I said the ch is working fine. It's just the call for hot water doesn't fire the boiler, and I'm not surprised as it appears the live to the grundfos is connected to the upstairs thermostat.

I have seen another excellent diagram you did on here for somebody else, and think that is probably the approach I should take too.

Thanks for replying.

 

[stem]

In your first post, you don't seem to understand the difference between an immersion heater., which is an independent 3kW electric heater that should never be wired to a Nest.....



[In your photo, you even labelled a wire going to the Nest Heat link as coming from the immersion.]

....and a hot water cylinder thermostat, which is a switch that controls the temperature of water stored in a hot water cylinder that is heated by a boiler.



So from what you say below, I'm now assuming that your original reference to an "immersion heater" was an error, and you actually meant a cylinder thermostat.

there is a thermostat on the water tank that appears to be wired into the water grundfos. I was suspecting that this link would need to be removed.

Regarding the above, the Nest provides time and temperature control of the central heating, but only time control of the hot water, so a hot water cylinder thermostat is still required to give control of the hot water temperature.

If I understand your post correctly, it appears that you maybe seriously considering removing a working cylinder thermostat leaving your hot water cycling continually without any temperature control and just wasting fuel.

I have seen another excellent diagram you did on here for somebody else, and think that is probably the approach I should take too.

I don't ever recall making a diagram that would work with what you have.

 

[Ohinever]

Sorry if my first post wasn't clear.

I never thought that power to the immersion heater was anything other than independent. I was refering the thermostat.

And I wasn't planning on leaving the hot water cycling at all. I was wondering if it would be simpler to turn it over to a timed on/off as I didn't think there was a way to integrate the cylinder thermostat with nest.

 

[Echo the husky]

I was wondering if it would be simpler to turn it over to a timed on/off as I didn't think there was a way to integrate the cylinder thermostat with nest.

Please call in a professional, you NEED the cylinder thermostat.

 

[stem]

I didn't think there was a way to integrate the cylinder thermostat with nest.

It features quite prominently in the Nest installation manual. S-Plan shown below.

Also to be considered:

I was wondering if it would be simpler to turn it over to a timed on/off

If the restrictions of your system do dictate that the hot water has to be 'on' in order to have the heating 'on' if you were to do that, then the heating would go off along with it.

 

[Ohinever]

Thanks for help. I tidied up the wiring and realise the link between 2 and 5 was broken. Replaced this wire. Now have cylinder thermostat in 6 as above, Essentially I have copied the old wiring from the Horstmann to the heatlink allowing for the different terminals.

Now everything seems to work. Can have heating on independent of hot water and vice versa, or both simultaneously.

One other question if I may. The horstmann had an independent frost thermostat. I presume this is not needed because it is taken care of by the nest itself with its low temp protection?

 

[ericmark]

It would depend where the frost thermostat and Nest thermostat is located. Some times the frost thermostat is in a garage with the boiler i.e. coldest part of system when not running, in this house with central heating run once a day for just one hour it would stop freezing, in last house it would need to run at least 4 times a day, as garage does not get that warm. Also this house no water in loft space, last house there was, so it all depends on layout.

 

[Ohinever]

It would depend where the frost thermostat and Nest thermostat is located. Some times the frost thermostat is in a garage with the boiler i.e. coldest part of system when not running, in this house with central heating run once a day for just one hour it would stop freezing, in last house it would need to run at least 4 times a day, as garage does not get that warm. Also this house no water in loft space, last house there was, so it all depends on layout.

Thanks. The boiler is in the garage.

Presumably then I need the horstmann frost start. Just to check this would be live to common 2 and com to c. H. 3 on the nest?

 

[ericmark]

Thanks. The boiler is in the garage.

Presumably then I need the horstmann frost start. Just to check this would be live to common 2 and com to c. H. 3 on the nest?

Unless built into boiler.