Central heating timer replacement

[DrPhill]

Hi there all,. Any central heating experts around?

I just wanted to know if my timer - Drayton (nee AES) LP111 can easily be replaced by a thermostat timer.

It is not in the ideal position for a thermostat, but it will do. I don't want to do a lot of rewiring as the boiler is on its last legs and due to be replaced. The last time I did this (a previous house 20+ years ago) I just took the old box off the wall and wired the new one in. I had some instructions from the manufacturer which helped. There were only four wires involved, one of which was hot IIRC.

Drayton have the wiring diagram for their new boxes but not for their simpler timer boxes. The new box has four wires, one of which is live. As my existing timer has a display (and no battery?) I guess it must draw power from a live wire suggesting that it, too, will have four wires like all the rest. If I can identify those wires on the old unit, I can just connect them to the new unit.

Does this sound feasible? Or are there some hidden complexities that I am missing?

Thanks in advance for any help.

Phill

 

[RogerS]

I don't see why not

This is the diagram for your LP111

 

[novocaine]

You could go with a wireless thermostat. Then the control box is where your timer is and the thermostat is where it should be.

Obviously just a suggestion and not what you asked. Perhaps take your timer off and have a look at what's there first. Take a picture and we maybe able to help.

 

[DrPhill]

Thanks Roger, Novocaine,

@Roger: Thanks for the wiring diagram - just what I needed to confirm the wires when I remove the old one.

@Novocaine: I had not thought of that... good idea. I will need to look at costs. I assume that the two units have a private communication method - not requiring my WiFi or similar? I will take a picture when I can get to the screw under the box. There is some junk in the way that needs to be moved. Preferably when it will not 'be making another mess'. SWMBO works on Fridays, I dont.....;-)

 

[Deejay]

Morning Phill

I have a 1994 model Randall 102e timer which I recovered from my present house. It ran a room stat controlled heating system and a DHW cylinder contolled by a cylinder stat.

I can't find any installation instructions but the web showed a Danfoss (who I believe took over Randall) 102e5. This is the PDF ...View attachment Randall Timer.pdf


The wiring shown on page 6 looks similar to your present timer. The text by the terminals looks like it should be DHW ,HTG, COM, N and L on pins 1 - 5 resp.

The operating instructions are here ...View attachment Time-Clock-Instructions-Danfoss.pdf

Let me know if you want it and I'll check if it still works.

Cheers

Dave

 

[sunnybob]

call me confused, but what is the actual problem?
I assume there is a thermostat on the timer, so is it broken?
If the boiler is due to be replaced wouldnt it be better to wait and get a dedicated one for the new boiler?

The simplest way of fitting a thermostat to your existing would be to buy a very simple thermostat switch and wire it between your existing timer and the boiler. Then the boiler would only work if the stat called for heat.
https://www.ebay.co.uk/itm/15-C-to-160- ... W6wkztGXWg

 

[loftyhermes]

What Bob said, fit the thermostat between the timer and boiler, that's what I did with mine.

 

[RogerS]

What Bob said, fit the thermostat between the timer and boiler, that's what I did with mine.

I think that both you and Bob have missed a key point in the OP.

Phill has an existing timer and he wants to replace it with a combined timer AND thermostat. For him to do what you are both suggesting means messing about with getting the switched live from out of his existing timer and then into the thermostat...mounted how ? In any case he says that the position for the thermostat is not ideal.

The suggestion of using a wired stat is ideal for him as it combines what you guys are suggesting...ie insert the thermostat between the switched live from the timer and his boiler. Then he can position the wireless thermostat sensor wherever is best.

 

[sunnybob]

The point that I havent missed is that the boiler is about to get changed. The new boiler should ideally have a same make thermostat set in a more relevant position.

If the entire thing is going to be changed out in a very short while, the three quid "get of jail" 1 wire cut and paste option I suggested is the logical route.

 

[novocaine]

Boilers dont come with seperate thermostats.
You have to buy one. Doesnt matter who makes the boiler, you pick the thermostat and timer thay meets your requirements.

I like honeywell.
My plumber friend likes drayton.
My BIL thinks his hive is the best (because he's a gadget lover).

No reason you cant do that now and use it on the next boiler.

 

[llangatwgnedd]

Save money, just get a energy efficient new boiler with timer built in and remote thermostat.

Problem solved

 

[RogerS]

Save money, just get a energy efficient new boiler ...

But there's the "Con". The myth. These so-called efficient condensing boilers claiming all that ultra-high efficiency are missing out on a little detail. Namely that they are that efficient only when they are condensing. But condensing stops around 55 degrees C and no-one runs their radiator based systems at that low temperature.

 

[jimmy_s]

Condensing boilers condense if they are directly weather compensated (condense for good part of year) or the heating is designed properly with a low return water temp. Problem is most of the stuff sold in the UK either has basic controls or designed on high flow/ return temp.

 

[DrPhill]

Lots of good thoughts here.....

Yes the boiler is on its last legs - but it may stagger through another year. And who knows, we might decide to move and leave the fun to the new owner.

The idea was, as mentioned above, to find a halfway cost/effort solution to controlling the boiler that we could reuse if/when the boiler is replaced. If we decide to stay in this house then we would likely do more than just replace the boiler - the house could do with a bit or rearranging, and the boiler could wind up in a completely different location, the pipework could change, etc,etc. Were we younger and more resilient then that is definitely the way we would go. Now the pain/payback equation looks a bit more finely balanced and we are dithering.

I dont understand this bit about condensing boilers only working below a certain temperature..... can anyone explain it to me, or point me to an article? I did not realise that this was a thing, and I reckon I should know a bit more.

 

[RogerS]

Does this help ?
https://www.wallhungboilers.com/news/13 ... 202005.pdf

 

[jimmy_s]

A condensing boiler works by allowing the flue gas to condense within the heat exchanger thereby extracting a chunk of latent heat which would otherwise be exhausted as steam in the flue gas. Water vapour being formed during the combustion process.

Traditionally systems in the UK are designed as 80 deg C flow / 70 return. Issue is condensation in the boiler heat exchanger is mainly dependent on return water temperature and 70 deg C is above the dew point of the water vapour in the flue gas. As the majority of boilers run at constant flow temp in the UK, they simply never condense apart from a few minutes when they first start.

Best bet is to either design system with a high temp drop and/ or a reduced flow temperature to try and ensure a return water temp of 55 deg C or lower for as much of heating season as possible. To maximise efficiency a weather compensated boiler is a good idea as the heating flow temperature is scheduled against outside temperature so if its warm outside the boiler flow temp is reduced and the overall heat output from the heat emitters is reduced. This means any TRV's fitted can control better also.

This combined with prioritised domestic hot water heating where the boiler switches from heating to ramping up to full fire to satisfy the hot water cylinder before reverting back to space heating is quite efficient.

This can be used along with other controls strategies such as night setback or optimised start etc depending on the system design etc but works well on its own.

 

[RogerS]

Jimmy, if I see a load of water vapour coming out of my oil boiler when it's running - then that is good or bad ?

 

[jimmy_s]

Sorry Roger - was away from computer

Is it a condensing oil boiler or conventional? If the flue is pluming then the water vapour in the flue gas is reaching its dewpoint as it exits the flue.

You might be getting some condensing in the boiler heat exchanger - ok in theory if its designed for this otherwise not so great. Condensate from oil is more acidic, mainly due to the sulfur content in the heating oil. In commercial heating systems somtimes there are pumps to rise the return water temp to prevent corrosion to the return side of the heat exchanger.

 

[sunnybob]

Weirdly, that did help me because I have a baxi luna boiler for my CH. =D>
Most of the technical stuff passed over my head though :roll:

I hear that the UK wants to ban all gas domestic boilers anyway. :shock:

 

[RogerS]

Sorry Roger - was away from computer

Is it a condensing oil boiler or conventional? If the flue is pluming then the water vapour in the flue gas is reaching its dewpoint as it exits the flue.

You might be getting some condensing in the boiler heat exchanger - ok in theory if its designed for this otherwise not so great. Condensate from oil is more acidic, mainly due to the sulfur content in the heating oil. In commercial heating systems somtimes there are pumps to rise the return water temp to prevent corrosion to the return side of the heat exchanger.

It's a condensing oil boiler.