Is my bypass switch wiring correct for a room thermostat ?

[eclat]

Hi,

I am new here and I have posted my question elsewhere, but have not gotten an answer so far. Here's hoping this site can do better

Not long ago I installed a wireless room thermostat for my central heating which is from a gas fired boiler without a hot water storage tank. The boiler have a built in thermostat and before installing the wireless room thermostat, the heating was dependant on the boiler thermostat as to when to fire up.

Having installed a wireless room thermostat and using it for some time now, I would like to have the flexibility to choose in either using the wireless room thermostat to call for heat or to have the ability to BYPASS THE WIRELESS ROOM THERMOSTAT AND THUS DISABLING IT so that the boiler thermostat is used instead.

My existing and proposed wiring is as follows:
From the mains, live, neutral and earth wires goes to the room thermostat relay box and from the relay box to the central heating boiler.

If I add a switch between the mains and the thermostat relay, will this work ? I attached my sketch of what I have in mind as to where the switch is added and the wiring that will be connected.

In the wiring diagram, if I flip the switch to position A, then the thermostat will be the one to decide when to fire up the boiler. If I flip the switch to position B, then the thermostat relay box will be disabled, but a connection is made directly to the boiler from the mains.

I just need to double check if my wiring is correct for this purpose and if it's safe.

Any comments or suggestions greatly appreciated and please don't hesitate to ask if any questions. Many thanks in advanced. View media item 59437

 

[JohnD]

You mean you want a "permanent on" switch to run the heating even when the house is warm, right?


Why?


BTW your diagram is almost certainly wrong and dangerous, but I don't know what boiler and controls you have or how it is now, or should be now, wired.

Your diagram suggests that the Central Heating room thermostat would cut power to the entire system and prevent the Hot Water from working, which is obviously absurd. You have also forgotten to show the heating timer.

 

[eclat]

You mean you want a "permanent on" switch to run the heating even when the house is warm, right?


Why?


BTW your diagram is almost certainly wrong and dangerous, but I don't know what boiler and controls you have or how it is now, or should be now, wired

Thanks for your reply. Yes I want a "permanent on" switch as a standby in case the thermostat relay fails when the weather is cold. I can then switch the heater on/off at the mains, and the built-in thermostat in the Ideal Elan boiler will regulate the room temperature as it had done for many years before I had the wireless room stat installed last year. Before the wireless stat was installed, there was a timer, but this was replaced by the wireless room thermostat.

The existing wiring is without the proposed switch in the diagram. The live and neutral from the mains 3 pin plug goes into the Honeywell CM927 wireless thermostat relay and from the relay to the 2 wires from the Ideal Elan boiler. The Elan Boiler is a old boiler that only serve the central heating and this is one of those that fires up just to heat the water for the radiators without a storage tank. Is this called a condenser boiler or something similar ? It's not a combi because I have a separate boiler for the hot water.

Hope these info helps and thanks. So how do I add the switch that will be safe ?

 

[Lectrician]

The boiler stat will prevent overheating, but I do question if this is really required.

You have over-complicated your diagram in my opinion. While it will work, all you need to do is this:

Untitled

• Lectrician
• 3 Apr 2013
• 1

The thing is, this should hardly ever go wrong, and if it does, you could just bridge the connection with a short piece of cable until you have a replacement.

 

[eclat]

The boiler stat will prevent overheating, but I do question if this is really required.

You have over-complicated your diagram in my opinion. While it will work, all you need to do is this:

Untitled

• Lectrician
• 3 Apr 2013
• 1

The thing is, this should hardly ever go wrong, and if it does, you could just bridge the connection with a short piece of cable until you have a replacement.

Thank you so much for your suggestion. I like the way you reuse my diagram.Just a couple of questions:
1) Does this mean all I have to get is a on/off switch ? And
2) before I go on a wild goose chase for something that may not be available, is there one switch for low voltage use and another for high voltage in the market or there is only one type for any use ?

I hope you are right that this (stat) should hardly go wrong, but there is also the situation of not having any new batteries in the house when you need it even when you get some standby for this purpose, but somehow ended up being used for something else. But most importantly, this setup will be handy until a replacement relay at a affordable price (such as betting on ebay), can be found, being on a tight budget.

 

[twgas]

Do you have 2 boilers? One for normal use and one 'in case it breaks down'. Adding the switch you propose is pointless!!!

 

[eclat]

Do you have 2 boilers? One for normal use and one 'in case it breaks down'. Adding the switch you propose is pointless!!!

Yes, 1 boiler for hot water and 1 for heating. Not 2 boilers for heating

 

[twgas]

Do you have 2 boilers? One for normal use and one 'in case it breaks down'. Adding the switch you propose is pointless!!!

Yes, 1 boiler for hot water and 1 for heating. Not 2 boilers for heating

OK my ? Is in the wrong place, it should read

Do you have 2 boilers One for normal use and one 'in case it breaks down'? Adding the switch you propose is pointless!!! - note the moved ?

 

[eclat]

Do you have 2 boilers? One for normal use and one 'in case it breaks down'. Adding the switch you propose is pointless!!!

Yes, 1 boiler for hot water and 1 for heating. Not 2 boilers for heating

OK my ? Is in the wrong place, it should read

Do you have 2 boilers One for normal use and one 'in case it breaks down'? Adding the switch you propose is pointless!!! - note the moved ?

Sorry - you lost me.

 

[ianmcd]

This is a complete waste of time if your wireless stat fails either as you have already been advised short the terminals with a short piece of wire or simply press the over ride button on the receiver which nearly all wireless room stats have

 

[eclat]

This is a complete waste of time if your wireless stat fails either as you have already been advised short the terminals with a short piece of wire or simply press the over ride button on the receiver which nearly all wireless room stats have

What is a waste of time ? the question about whether I have 2 heating boilers or my posting on wishing to install a bypass switch ?

If you are referring to the 2 boiler question, I tend to agree.

 

[D_Hailsham]

I want a "permanent on" switch as a standby in case the thermostat relay fails when the weather is cold.

You don't say which wireless stat you have, but the Relay box of my Honeywell CM927 has been working for the last six years without a fault.

As for batteries, I am now on the third set, the previous two sets lasted about three years each. You need good ones, i.e Duracell.

There should be a setting to determine how the relay works if it loses communication with the controller (e.g dead batteries). On the CM927 it can automatically go into a 20%/80% on/off cycle.

 

[eclat]

I want a "permanent on" switch as a standby in case the thermostat relay fails when the weather is cold.

You don't say which wireless stat you have, but the Relay box of my Honeywell CM927 has been working for the last six years without a fault.

As for batteries, I am now on the third set, the previous two sets lasted about three years each. You need good ones, i.e Duracell.

There should be a setting to determine how the relay works if it loses communication with the controller (e.g dead batteries). On the CM927 it can automatically go into a 20%/80% on/off cycle.

Thanks for your comments. I did mentioned which stat I have in my very first reply, whichI is the same as the one you have, the CM927. However, I am trying to cater of all eventuallities given that if there is a fault, it would be a simple alternative than working in the cold or looking to get some new batteries. But I hope the unit I have is as reliable as the one you have. Who knows, with modern manufacturing these days

 

[D_Hailsham]

I did mentioned which stat I have in my very first reply, whichI is the same as the one you have, the CM927.

Missed that!

However, I am trying to cater of all eventualities given that if there is a fault, it would be a simple alternative than working in the cold or looking to get some new batteries.

Just set Cat 2 System Parameter 7:LC to 1. The boiler will automatically go into a 20% on / 80% off routine if communication is ever lost.

You don't seem to have much faith in modern technology. Is that due to a bad experience?

 

[CBF]

way to go to over complicate things, total waste of time, are you going to put another switch in just incase the first one you fit goes wrong & then another & another