Worcester Greenstar 24RI with Honeywell Sundial Programmer

[IanBorn1973]

Hi all,

I had a new boiler (Worcester Greenstar 24RI) fitted about 5 years ago when I had an extension built which replaced on old Potterton boiler. The old Programmer was moved across which was a Honeywell ST6400.

I bought a few years back a Honeywell Sundial Pack 2 which has the added benefit of a Wireless room stat which I have not had before and just used programmed on/off times only. I chose the Sundial because it was a direct replacement for the 6400 and meant no need to call out an electrician or plumber because the back plate wiring would stay the same. for some reason I never got around to swapping out and finally did a couple of weeks ago but I think this "No wring changes needed" is a red herring.

The old system under the ST6400 worked seamlessly and included a pump overrun feature for when the heating turned off. What I have noticed is when the room stat turns off the boiler when the room temperature has been reached you hear a pressure noise which lasts for a few seconds and upon investigation i believe its due to the pump overrun not working when the stat turns off the boiler.

I have trawled the internet and there is mention of this being an easy fix with a single wire from the boiler but what I would like to ask is:

1. Is this the case and an easy competent DIYer fix, switch of electric and run a single bypass wire or something like that? or much more complex?
2. If not and I will go down the electrician route but want to check based on experience if the Sundial setup is the best product for a Worcester Boiler? Is there a better solution (product) which enables me to have a wireless room stat? even if that means spending a bit more and getting a new product and re-wire the whole thing? Im not bothered with these internet based controllers as don't see the point in paying a subscription to control your heating.

Thanks in Advance

 

[stem]

I chose the Sundial because it was a direct replacement for the 6400 and meant no need to call out an electrician or plumber because the back plate wiring would stay the same. for some reason I never got around to swapping out and finally did a couple of weeks ago but I think this "No wring changes needed" is a red herring.

They are identical, both programmers are just 'on' and 'off' switches and provide exactly the same functions from the same terminals as follows:

N. Neutral
L. Live
1. Hot water off (not always necessary depending on type of system)
2. Central heating off (not used)
3. Hot water on
4. Central heating on

What I have noticed is when the room stat turns off the boiler when the room temperature has been reached you hear a pressure noise which lasts for a few seconds and upon investigation i believe its due to the pump overrun not working when the stat turns off the boiler.

The pump is wired directly to the boiler [terminals LP (live pump) and NP (neutral pump)] so the boiler controls the pump overrun. All that the 6400 and the Sundial RF 2 do, is turn the heating and hot water 'on' and 'off'. They have no control of the pump overrun, nether do the thermostats.

If the pump overrun wasn't operating, then the boiler overheat would likely trip. The fact that you hear a noise suggests that the pump is still going. The noise is probably the system adjusting to the changing pressure in the system as the heating circuit closes down.

 

[IanBorn1973]

Thanks Stem for the information.

But surely the stat switching off the boiler when the set heat is reached is no different to the Boiler switching off at the set time like with my old controller?. Surely the pump overrun must be required because the water in the pipes and boiler is still hot so needs to keep running to cool.

Im no plumber so im not douubting what you are saying, i have watched the stat reach temperature and switch off boiler and heard the pump stop so it definately is not running, the sundial also by default switches the boiler back on every 10 mins after reaching temperature (i think its called cycle rate) so just wonder if this is happening is it damaging the boiler every time the boiler turns off without a pump overrun working with the stat?

 

[stem]

But surely the stat switching off the boiler when the set heat is reached is no different to the Boiler switching off at the set time like with my old controller?

Yes the stat switches off the boiler and the new one will be doing that exactly the same as the old one did. They both provide a simple on/off switch and that's it. There are no electronics inside either of them to control a pump overrun.

Surely the pump overrun must be required because the water in the pipes and boiler is still hot so needs to keep running to cool.

Not all boilers need a pump overrun and it is the boiler manufacturer that determines if is one is necessary or not. If one is necessary, it is the boiler manufacturer that provides the controls for it as part of the boiler. As I said before, the pump should be wired directly to the boiler where the boilers integral circuitry keeps the pump running until it has cooled.

Im no plumber

Neither am I. I'm an electrical engineer. But I have Gas Safe friends who get me to help them out from time to time when the controls installs are tricky, and troubleshooting.

I have watched the stat reach temperature and switch off boiler and heard the pump stop so it definitely is not running

In that case check that the pump is actually wired to the boiler terminals LP and NP. It may be that someone has incorrectly wired the pump, but changing the 6400 for the Sundial won't have had any effect on that, and unless someone has altered the wiring, it would have always been that way.

If it is wired to the boiler LP and NP and it isn't running on when the boiler goes off, then there is a problem with the boiler.

 

[IanBorn1973]

Thank again Stem, the control panel is easily excissible and is right by one of the pumps so i will turn of the electic and have a lok inside and see whats wired to what. If wired correctly i will drop an email to worcester and see what they say. Thanks for the help