Pump Overrun on Intergas OV18

[MJN]

I've currently got an Ideal Icos HE18 heat-only boiler and, seemingly somewhat surprisingly given what I've read about it, has never let me down. However, at 15 years old I know it is only a matter of time before it reaches the end of its life and so I thought I'd start looking at candidate replacements that will fit within the current setup.

One boiler that caught my eye is the Intergas OV18, particularly due to its Opentherm support. I was wondering about pump overrun though as I see from the installation instructions that is appears to require it (set by default to 1 minute after demand) however the example wiring schematics (on page 52) appear to suggest that the pump doesn't have to be connected directly to the boiler but can instead be connected to the switched lived in the wiring centre. However, if wired this way how would the pump overrun be achieved, given that at the end of a demand from a zone valve the boiler would have no means to overrun the pump?

On an unrelated subject, can the OV18 be used on a sealed system? The instructions only discuss open vent but I note the specs say it can work up to 2.5 bar.

P.S. Are there any Intergas installers here that cover the Wiltshire/South Gloucestershire area? I've always figured that anyone interesting enough to discuss boilers and heating systems outside of the day job is probably exactly the sort of person I'd want fitting a new boiler for me!

 

[sxturbo]

The OV can be used on sealed system.

I'm wondering if the opentherm side of things need the pump to be connected to the boiler, ive no idea though and can't answer you main question

 

[MJN]

Thanks sxturbo re the sealed system usage. Good point about a potential required for pump control with OT - not something I considered to be honest.

Incidentally, my preference for external (non-boiler) pump control was to avoid having to deal with the consequences of the S-plan setup and avoiding faffing with bypass valves.

 

[sxturbo]

I don't think there is any issues with the s-plan arrangement.

It's probably better with opentherm as you have to have either hot water, or heating, usually hot water is set as priority.

You can have a sealed system boiler with a built in pump and still keep the s plan setup.

 

[MJN]

For some reason I've got something against automatic bypass valves - not sure where that's come from though. I suppose if it is properly set up then it'll only kick in when the CH and HW zone valves are closed and thus not introduce inefficiencies. (With the CH on I've got two radiators without TRVs so don't require one then)

 

[muggles]

There's no requirement for a pump overrun on the 18OV, it's just there as an option. For Wiltshire/south Gloucestershire, use Dominic Eves at Pure Boilers https://pureboilers.co.uk/ and you'll get a top quality installation. Used to be my stomping ground too, but I've since moved away

 

[MJN]

Thank you both. And thanks muggles for the recommendation - I've bookmarked Dominic's site (which looks good, and includes coverage on Opentherm so that's a good sign). That's the installer selected, just need to think a bit more about candidate boilers! I won't waste Dominic's time now whilst I'm just kicking the tyres but will see what he recommends nearer the time.

 

[MJN]

To update; I couldn't help but get in touch with Dominic and whilst admitting I am just kicking the tyres at the moment he got back to me straight away and gave me some food for thought about a couple of things including changing the S-plan setup to HW-priority to make the most of Opentherm and our fast recovery cylinder. I think that's the installer and boiler selected so now just need to decide when - wait until the Ideal Icos starts to give us grief or go for an upgrade sooner rather than later? I'm tempted by the latter, particularly as I'll be renovating the room it is in a few month's time so it seems an ideal time to take that opportunity to run any additional cabling at the same time.

 

[muggles]

If you've got imminent renovation plans then now is the time to do it, certainly. Might be a day or two without heating though

 

[MJN]

Yeah, I'm sure that's doable. I'd rather be replacing it in spring/summer out of planned choice rather than due to catastrophic failure the week before Christmas which would otherwise be just my luck (shouldn't tempt fate given that's where we are!).

 

[Ethel H]

...changing the S-plan setup to HW-priority...

To achieve hot water priority, my understanding is you can keep your S-plan heating system and it will only require a little rewiring to achieve hot water priority. This method is called "X-plan", I believe this term was coined by Intergas themselves.

The normal approach to HW priority was to use a W-plan heating system i.e. with a 3 port diverter valve.

Intergas have recently outlined their own favored approach to hot water priority called X-plan which is based on the S-plan heating system but with a little rewiring. They haven't explained why they prefer X plan to W plan, perhaps it is more robust?

Here is some material I found about X-plan sourced from Intergas and the Intergas Shop, including a couple of wiring diagram pdfs.
https://www.facebook.com/TheInterga...-on-a-joule-high-gain-cylind/437315390390480/
https://www.intergasheating.co.uk/consumer/2019/11/05/tech-talk-3/

 

[MJN]

Yes, the heating guy Muggles recommended was also suggesting rewiring to so-called X-plan and as you say it does seem to be a term coined by Intergas. Note however that it's not just a rewire - it also requires replacing the normally-closed CH zone valve with a normally-open one. This is closed only when there's a HW demand so that the cylinder can be reheated at full pelt without overdoing things on the CH side. Conveniently this is gives a pathway for pump overrun without requiring an autobypass (although it could result in heated water being dumped into the radiators during the summer months but it shouldn't overrun for long (1min by default on the OV18).