From a seperate thermostat and programmer to one unit

[Tyzerx]

Hi All.

I recently found out my thermometer (Honeywell) dial is not working so I am looking to replace (located on landing).

We have a Potterton programmer EP2001 by the boiler. You cannot set seperate on and offs times for the HW and CW.

My question is to be able to set seperate on and off times, I want to get a new programmer. I see now you can get a thermostat and programmer in one device.

Is it as easy as switching off the Potterton, installing new thermometer and programmer on landing?

Or is there actual wiring changes that need to happen making this job more complexed...

Thanks for your help!

 

[terryplumb]

More to it than you think. Plumbing and wiring will need altering .

 

[fixitflav]

Hi All.

I recently found out my thermometer (Honeywell) dial is not working so I am looking to replace (located on landing).

We have a Potterton programmer EP2001 by the boiler. You cannot set seperate on and offs times for the HW and CW.

My question is to be able to set seperate on and off times, I want to get a new programmer. I see now you can get a thermostat and programmer in one device.

Is it as easy as switching off the Potterton, installing new thermometer and programmer on landing?

Or is there actual wiring changes that need to happen making this job more complexed...

Thanks for your help!

If you have a mid-position diverter valve (Honeywell Y-plan) or 2 separate valves (Honeywell S-plan) you can have HW or CH. If you have an either/or diverter valve (Honeywell W-plan) you can have HW only or HW + CH, but not CH only, whatever the programer does.

 

[D_Hailsham]

If you have a mid-position diverter valve (Honeywell Y-plan) or 2 separate valves (Honeywell S-plan) you can have HW or CH.

Correct

If you have an either/or diverter valve (Honeywell W-plan) you can have HW only or HW + CH, but not CH only, whatever the programer does.

Incorrect.

W Plan is fully pumped with hot water priority so you can have HW or CH, just as with a Y plan or S Plan.

 

[fixitflav]

W Plan is fully pumped with hot water priority

On W-plan the cylinder stat must be satisfied before the diverter valve can move to the CH position. The only way you can have CH without HW is to turn the cylinder stat right down so it's always satisfied. You can't set up the programmer for CH but not HW. If what you said, that the W-plan works just like the Y or S-plan, were correct, what would be the point in using a mid-position valve, which is more complicated and expensive? And probably less reliable.

 

[D_Hailsham]

On W-plan the cylinder stat must be satisfied before the diverter valve can move to the CH position. The only way you can have CH without HW is to turn the cylinder stat right down so it's always satisfied. You can't set up the programmer for CH but not HW. If what you said, that the W-plan works just like the Y or S-plan, were correct, what would be the point in using a mid-position valve, which is more complicated and expensive? And probably less reliable.

First you mention a diverter valve, then you talk about a mid-position valve, which is irrelevant. The W-plan uses a diverter valve (e.g Honeywell V4044C) not a mid-position valve.

Here is the wiring diagram for a W-plan. Run through all the options and you will see that CH without HW is possible, even if the cylinder stat is not right down. "Without HW" means HW is off at the programmer. If HW is on then it automatically has priority.

 

[fixitflav]

First you mention a diverter valve, then you talk about a mid-position valve, which is irrelevant. The W-plan uses a diverter valve (e.g Honeywell V4044C) not a mid-position valve.

Here is the wiring diagram for a W-plan. Run through all the options and you will see that CH without HW is possible, even if the cylinder stat is not right down. "Without HW" means HW is off at the programmer. If HW is on then it automatically has priority.

Whether you call a mid-position valve a diverter valve or not is irrelevant, they're both 3-port valves and everybody knows the difference.

You need to study the wiring diagram. The only way CH can take place is when the diverter valve is energised. This happens via the cylinder stat, when contact 2 is made, which is when the cylinder stat is satisfied. If the cylinder stat is calling there is no CH. The time controller must be set up so HW or HW + HTG is powered. In some respects it's like the old gravity HW, pumped CH systems, where for HW the boiler is energised, for CH the pump is also energised, but you get HW as well, whether you want it or not.
I repeat my question - why install a Y or S-plan system if the W-plan does the same with simpler kit?

 

[stem]

We have a Potterton programmer EP2001 by the boiler. You cannot set separate on and off times for the HW and CW. My question is to be able to set separate on and off times, I want to get a new programmer

The EP2 is well capable of having separate on & off times. If it doesn't allow you to do this presently, that is because it has been set in 'Gravity System Mode' changing the setting to 'Fully Pumped' will allow the programmer to have separate times for the heating and hot water.....

......However, as has been stated, likely you have a system with antiquated plumbing that doesn't support separate control (ie one where the hot water has to be on in order for the heating to work) so the programmer has been 'dumbed down' accordingly.

 

[fixitflav]

However, as has been stated, likely you have a system with antiquated plumbing

It seems a bit bit strong to describe W-plan as antiquated, similar to gravity HW. With gravity HW, unless there are additional controls, if you want HW on, the boiler is constantly powered, so cycling On/Off as the heat is lost up the flue, even when the cylinder is up to temperature. W-plan avoids that.
Also if there is outdoor temperature compensation, the boiler control-stat setting might be too low to heat the cylinder, so the system has to go to HW only, with default control-stat setting. In that case a mid-position valve is redundant.

 

[stem]

It seems a bit bit strong to describe W-plan as antiquated

Unless I missed it, the OP hasn't actually confirmed he has a W-Plan (and let's face it, they are quite rare) and I did say:

likely you have a system with antiquated plumbing

In addition, a W-Plan would have allowed the EP2 to have separate heating and hot water times, so wouldn't have required to be restricted when originally installed.

 

[D_Hailsham]

You need to study the wiring diagram. The only way CH can take place is when the diverter valve is energised. This happens via the cylinder stat, when contact 2 is made, which is when the cylinder stat is satisfied.

I see what you mean. Thanks for pointing. it out

 

[fixitflav]

I see what you mean. Thanks for pointing. it out

No problem! Glad we sorted it.

 

[D_Hailsham]

In addition, a W-Plan would have allowed the EP2 to have separate heating and hot water times,

That's what Honeywell say in the FAQ on W-Plan systems: "Hot Water and Heating can be independently timed, however the nature of the system will ensure that the indirect hot water cylinder is always up to temperature."

I don't see how it would work.

 

[fixitflav]

Unless I missed it, the OP hasn't actually confirmed he has a W-Plan

That's right, the OP hasn't been back at all. Most likely he has, or an even older gravity HW system, or the old programmer would not have been set up the way it was. I was jumping the gun assuming you were lumping W-plan in with gravity HW!

In addition, a W-Plan would have allowed the EP2 to have separate heating and hot water times, so wouldn't have required to be restricted when originally installed.

I'm not with you there. W-plan cannot have separate HW and CH, it can have HW only, or HW+CH, and the programmer must be set up accordingly. As I've explained in a couple of posts.

 

[fixitflav]

That's what Honeywell say in the FAQ on W-Plan systems: "Hot Water and Heating can be independently timed, however the nature of the system will ensure that the indirect hot water cylinder is always up to temperature."

I don't see how it would work.

Neither do I. Going back to the W-plan wiring diagram, when HTG only is energised at the progammer, if the cylinder stat is calling the cylinder will be heated, and CH only start when the cylinder stat is satisfied (if the roomstat is calling, obvs). So if somebody wanted to work on the cylinder, set it up that way and left it for a few days, assuming the cylinder would have cooled, he would get a surprise!
Crazy thing to do anyway. That way, when calling for CH, there's likely a delay waiting for the cylinder to heat up (depending on the HW time settings). Best way IMO is to have HW 24/7, (HW+) CH as required (I run my CH 24/7 as well, but that's just me), then when CH is called it usually comes on immediately. And as a principle it doesn't seem good practice for the system to give HW, when CH is requested. Maybe OK here, but that sort of thing can cause accidents!