Central heating programmer

[milliesdad]

I have a 'van with an Alde central heating set up. The boiler is controlled by a simple on off switch and the pump for heating by a programmable thermostat. We set the night temp to 15 and the day temp to 20., but in order to wake up to a nice warm 'van we must keep the boiler switched on all night. the boiler then turns itself on and off during the night to top up the hot water which is a) wasteful and b) quite noisy.

I would like to install a domestic type of programmer to be able to independently control the heating and hot water but all units are mains powered.

So my questions for you electrical wizards are: -

1. Is there a battery or 12v powered programmer on the market, or

2. How can i convert a domestic 240v type to work on battrey or 12v? (bypassing the transformer perhaps?)

I am good with a soldering iron but it's been 20 years since i did electrical principles at tech so i'm a bit rusty on the theory now.

Any help much appreciated.

Many thanks

Stewart.

 

[Rod_5041370]

A mains programmer can't use much power so a small 12vdcto 230vac inverter should do the job.

 

[chrisn7]

Hello Stewart

I am surprised that you have found the Alde unit unsatisafctory. This unit is different from a typical domestic unit.

Firstly, it always in an 'On' condition, and kicks in like a domestic room thermostat when the temperature falls below the value you programmed in.

Secondly, the times that you programme in are not 'On/off' times like the domestic unit. Instead they control the period for which you require the set *temperature* to prevail.

To illustrate, if you set your temp of 20 from say 07.00, the system will change at that time from maintaining the night setting of 15 to your day setting of 20. However, if the sun is shining and the van temp is already at 20, then it will not kick in.

During the night, you could reduce the setting of the thermostat mounted on the boiler itself, which might help with the no of on'off cycles ?

The boiler always heats the hot water when the c/heating is operating, so changing the programmer will have no effect...

 

[milliesdad]

Hi Chris, thanks for taking the time to post.

I'm not dissatisfied with the Alde unit - it works very well. Let me try to explain with an example.

We set the night temp to 15 with the day temp (from 7 am) to 20. So during winter aurumn and spring we just leave it on all the time and are nice and comfy.

Let's say the night temp goes down to 16 - still comfy at night but a little chilly to get up to so at 7 am the heating comes on to bring the taemp up to 20 fro when we get up.

In order for the heating to come on the boiler on switch must be on all night. The boilers turns on and off throughout the night as the domestic hot water cools, even though we don't need it for the heating until the morning. Obviously we don't need hot water during the night so it is a waste of gas.

What i'm looking to achieve is separate control of the heating and water with the heating switching on the boiler when required (kind of over riding the water setting)

Think of it as 2 time switches - 1 for the heating (with a thermostat) and 1 for the boiler. The heating switch will operate the pump and boiler and the water switch just the boiler only. A domestic unit will do this but requires 240 volt hence the problem.

I should have said that we use CLs and CSs and very rarely use EHU.

I hope this explains my problem a little beter.

Thanks again.

 

[Garfield]

We use an avensis/Drayton digistat 2 which is a 24h programmable room thermostat that runs off a 9v battery and will switch whatever voltage, up to 240v, is attached.

I'm unfamiliar with your heating system but can't you just turn the hot water temp right down overnight?

 

[gary]

I'm fairly sure at least with the 3000 series, the programmer contains the van temperature control so not an option to change it.

Surely then the simple answer is to use a second timer to cut the 12 volt supply to the heater before the main on/off switch?

 

[milliesdad]

You're right Gary, so i was going to keep a thermostat in the circuit (as with a domestic system.)

I did think of a timer for the hot water but the heating timer would need to over ride it otherwise the pump would run and the boiler wouldn't. To wire it up for this and not have the boiler timer also switching on the heating would mean wiring in diodes and resistors and as i said my electrical theory is a little rusty. A domestic programmer made to work off 12v would be perfect - i just don't know how to do it.

Thanks for your input anyway.

 

[gary]

Yes my mistake, of course the programmer clock stops if all power is cut.

Thing is what exact model boiler are you actually talking about

 

[milliesdad]

Hi Gary, it's the compact 3000.

 

[chrisn7]

Hi Stewart

I don't believe it matters what you do with programmers. When the water is heated, this in turn heats the fuid in the c/heating system, which is an ethylene glycol mix, identical to car antifreeze. Therefore you can't have the c/heating systen on without heating the water

 

[Alan_374306016]

Hi my 2 pennyworth - Screwfix sells various programmable stats - I've got Horstmann myself. The stat is battery operated, 3 AA, & just acts as a relay switching on whatever is connected to it. There are 7 day and 5 day versions, which means that you can programme different settings for different days of the week - probably not required in your 'van.

 

[gary]

Going back to what I said before, the simple answer is to kill power to the heater with a timer and it seems from above there are several suitable timers available.

The problem then of the main timer clock stopping can be overcome by cutting the 12v feed wire from the boiler and connecting the timer side to a permanent 12v feed.

To tidy the job up, this arrangement could be through a switch, whereby the 12v to the main timer can be switched at will from original supply from boiler to independent supply.

Always remembering any supply should be suitably fused, 2A in this case I think

 

[Val & Frank]

Hi Millies dad,

You been away ?????

We have the Alde 3000 pretty good system, regret showing Val the temp control now the vans at 30 + when we wake up !!!!.

Val & Frank

 

[chrisn7]

In the original post, Stewart stated that he wanted independent control of heating and hot water, but still wanted the heating available at night.

With this boiler, you can have water only. If you want heating, then you have to have hot water as well.

Without the hot water, there is simply no means of heating just the fluid in the heating system. Fiddling with programmers and wiring will achieve nothing

 

[milliesdad]

Hi all and thanks for your input.

I have now resolved the problem as follows :-

I have installed a new programmable thermostat in the bedroom and this controls the CH pump.

This also energises a relay whose contacts are wired in parallel with the boiler on off switch. Thus when the thermostat calls for heat it also turns on the boiler.

The original thermostat has also been wired in parallel with the boiler switch and thus can be used to time the water only to come on and off.

The boiler switch can still be used to override any timings if I need hot water at other times.

I knew there would be a solution - just took me a while to work it out!

Thanks all for your input.

Stewart.