Replace horstmann channelplus 37xl with Nest (3rd generation)

[andrew1949]

Hi Everyone,

Hope you can help me out with this, had a little trouble posting.

We have a condensing boiler with a mains pressure hot water cylinder.

At present there is no thermostat fitted to the system which relies on TRV's

As we have very long pipe runs with have a separate pump for the hot water.

The programmer is wired so that

CH Zone 1 switches the boiler for central heating
CH Zone 2 switches the boiler for hot water
HW switches the hot water circulation pump

I want to know how I should wire the heatlink

I think I will need to provide a separate switch for the HW pump

Any help gratefully received

Andrew

 

[stem]

HW switches the hot water circulation pump

I think I will need to provide a separate switch for the HW pump

I am assuming here that you are referring to a 'Secondary Hot Water Circulator' that circulates the domestic hot water around a ring main so that hot water is available instantly at each outlet, then the answer is yes you will need to move that to another timer. This is the first time I have come across this in a domestic property, but can understand why if you have an unusually long pipe run.

Here's one I did earlier:



Once the secondary circulation is out of the picture, the Zone 1* connections would be wired to the Central heating terminals of the Heatlink and Zone 2* connections to the Hot Water terminals. You should identify what each of the wires connected to the Horstmann does from the diagram you have posted, and then move them to the terminal that has the same function at the Heatlink.

You will have to link the terminals L, and the two 'commons' 2 & 5 together at the Heatlink. [This link is made internally in the Horstmann]

Finally at least one radiator in the room where the Nest Thermostat is located should not be fitted with a TRV, otherwise it could interfere with the operation of the Nest and prevent it working properly.

*Zone question.

The programmer is wired so that

CH Zone 1 switches the boiler for central heating
CH Zone 2 switches the boiler for hot water

Are you sure that CH Zone 1 switches the central heating? The way that the wires are connected would lead me to expect that to be the hot water. But hey, there's more than one way to skin a cat. If not, don't worry about it, all you are doing is moving wires from one controller to another that electrically speaking has the same switching functions, so if it works now, nothing will change. But you will need to make sure that the heating and hot water wiring goes to the right terminals at the Heatlink.

 

[andrew1949]

Many thanks stem for taking the trouble to answer my post, I really do appreciate it.

To answer your points yes it is a secondary hot water circulator, I did consider perhaps wiring it in with the hot water

but would prefer to have separate control over it.

Thank you for the heads up about linking the live and 2 and 5 on the heatlink , I supposed I should have realised that when I saw the terminals

but assumed it was linked internally as the Horstmann.

Zone 1 is definitely controlling the central heating.

The only thing I don't understand from the wiring diagram on the Horstmann is the Blue wire on the no 2 terminal.

I can understand the power coming into terminals 2 , 4, 6 and being switched to 1,3, and 5

Any idea or is it a question of tracing it and trying to discover what it does?

Andrew

 

[stem]

That's exactly the bit that made me question Zone 1's actual use. It's necessary to have a wire connected to the 'Hot water off' when the system incorporates a 3-Port valve [although two, 2-Port valves are more commonly used with a "mains pressure" hot water system (aka unvented) like yours and 2-port valves don't need that either]

I have only ever once come across a system with a 'central heating off' connection that contained a very uncommon type of motorised valve (MoMo, or Motor on, Motor off) that requires this connection to close it.

In reality, the blue wire may not be actually doing anything, but only the original installer would know. However as I said earlier, you are simply exchanging one electrical switch for another and the corresponding terminal at the Heatlink would be (1) Heating Satisfied.

I would be tempted to try and trace it to see what it's connected to, for my own curiosity as much as anything, or disconnect it and see if anything stops working.

It is better to have the circulation pump on a separate timer, as it may require different on times for actual usage of water, to those times selected for the actual heating up of the cylinder.

 

[andrew1949]

Hi stem thanks again for your speedy and very helpful reply.

That is a great point about the separate times for heating and usage of the water.

I may well leave the Horstmann in place to carry out that function, because in addition to timing, it has a advance and boost function.

I think you may well be correct with the blue wire, we have an Esbe 3 way valve with 1 port blanked off

When it is off or calling for hot water the indicator points to the blue section, when heat is required, whilst the boiler is initiating firing the valve turns to the red section, then several seconds later the heating circulation pump starts up.

Here's a pic of the valve, and "man" size circulation pump

Thanks again for your help


Andrew

 

[stem]

Makes sense. Probably the 'heating off' blue wire is being used to position the valve in the hot water position, which in effect with the planked port, is closing it as far as the central heating is concerned.

I suspect that this valve was there before the unvented hot water cylinder was installed, with the now blanked port feeding the cylinder. A new 2-port valve probably came with the cylinder which has been used and so the original 3 port valve hot water outlet was blanked off. So all looks good to me.

I guess that there is another pump somewhere for getting water from the boiler to the hot water cylinder.

That's some pump. More akin to an industrial installation. You must have a lot of radiators.

 

[andrew1949]

You are correct there is a separate pump taking hot water to the cylinder

That valve was installed when the heating was changed from oil to gas

We have 19 radiators but about 20 metres of "trench" heating which is pretty useless.

Thanks for all your help, I understand it all a lot more now and am prepared to give it a go

Andrew

 

[andrew1949]

Ok , I fitted the Nest and it did not work.

Leading on from our discussions I found this image of a similar Horstmann programmer and it made it clear to me what the problem is.

When the heating is off or when calling for hot water the blue wire carries a live feed which keeps the valve in the closed position allowing water from the boiler to the HW cylinder.

When you switch to heat the live feed is sent to the boiler, and taken from the valve which opens.

You cannot achieve this from the nest as the Heating satisfied only goes live when the temperature is reached.

So on reflection the only way I could use the Nest with my system would be to incorporate some sort of switching relay for the valve using a separate feed and letting the heat on from the Nest control it.

In the end it's not worth the bother.

Thanks for your help though this has all proved useful in learning how my system operates.

Andrew

 

[stem]

I'm not sure I understand what you mean by the above, because the switching elements of the Channelplus 37xl and the Heatlink work in exactly the same manner.

The only difference between the Channelplus 37xl and the Heatlink, is that the Channelplus 37xl 'common' contact is connected internally to the the 'live'. But with the Heatlink the 'common' terminal is outside of the unit and needs linking to the 'live' by the installer, as per my sketch below:

[This will also be the case with the "similar Horstmann programmer" in your last post. The reason common terminals are provided outside of the unit, rather than connected to 230v inside, is so that they can be used to switch other voltages (some boilers use 24v) if required]



Then, once the common at the Heatlink is connected, both devices will function identically to each other.

So, for both devices:

When heating is required, the common is connected to the 'On' terminal (Grey wire in your case)
When heating is not required the common contact moves across to the 'Off' terminal (Blue wire in your case)

When you installed the Heatlink did you add the external link between the L and Com (2) terminal?

[To keep it simple I haven't shown the hot water part but that would also need a link between the L and Com (5) terminal]

 

[andrew1949]

Hi stem, thank you for your continued interest.

Firstly let me confirm I did add a link between the live and the common on 2 & 5 on the heatlink.

Are you saying that with the heating off the the heat satisfied also has a voltage, in the way terminal 3 has on the Horstmann.

The reason I say this is because I connected the blue wire to this as your original instruction and the Nest never worked. I wondered if this only went live when the desired temperature was reached and it received a signal from the thermostat?


Is it possible that the motor can rotate in different directions by virtue of how it is wired

I'm wondering this due to the wiring indication that came with the valve, and also the number of wires in the connecting box.

Finally on the programmer what would be the point in providing term 3 to be live when the heating was off.

If this is indeed the case, I don't think I can use the Nest unless I use some sort of relay, or change the valve.

Thanks for your help, I think I must be pretty sad as I have found this all very interesting.

Andrew

 

[stem]

Are you saying that with the heating off the the heat satisfied also has a voltage, in the way terminal 3 has on the Horstmann.

Yes that's it exactly!

The contact inside the Channelplus comprises of a live central contact that moves between two fixed contacts, 'on' and 'off'. It moves from one, straight to the other so at any time, one of them will be live according to whether the Channelplus says tells the switch to be on or off.

The Nest is exactly the same. The central contact which is live (because of the link from live to terminal 2) also moves between two fixed contacts 'on' and 'off' according to whether the Nest says tells it to be on or off.

Of course the Nest will not only switch off when the time goes off, but also switch off when the correct temperature is reached, but the wiring doesn't know that, as far as it is concerned it's just going off.

Unfortunately, I don't know anything about the valve having never seen your particular type. But electrically speaking, the Channelplus and the Hive are just switches and are identical in their operation, so if your heating works with one, then there is no reason why it wouldn't work with the other.

So in summary, can you confirm that you wired the Heatlink as follows:

Neutral to (N)

Live to (L) and also connected by links to terminals (2) and (5)

The Grey wire in Channelplus Zone 1 CH On = Nest heating call for heat terminal (3)

The Blue wire in Channelplus Zone 1 CH Off = Nest heating satisfied terminal (1)

The Brown wire in Channelplus Zone 2 CH (HW) On = Nest hot water call for heat terminal (6)

 

[andrew1949]

That is precisely how I wired it

Knowing now that it should mimic the functions of the Horstmann I will give it another go when the weather warms up a bit.

I won't be very popular if i do it now and we don't have heating.

In the meantime I'll try to figure out the wiring and definitely trace that blue wire, and leave you in peace.

Thanks for all the advice and speedy responses

Andrew

 

[stem]

Hi Andrew thanks for the update. Strange why it didn't work, but understand why you wouldn't want to me risking a failure at the moment.