Immersion hot water system, what schedule is most optimal?

Bendy_House

Arfa__ said:

Pic from behind the lower cover on the tank:

Would I be right in saying there is only one immersion heater fitted here and that the top cover just has a blanking plate?

I think that's a fair assumption.

The upper immersion position is useful if you use an immersion heater regularly, but only wish to heat a half-tank. Obviously, tho', gas is the cheapest way to do this.

I can't read the position of that red 'stat arrow - is there a temp scale? Is it currently fully anti-clockwise? If so, that would kind of make sense, as set to what I guess will be around 40oC at that level, will mean MUCH hotter above - well above 60oC at the top of the cylinder where the hot water is drawn off.

(Why are there TWO cables going to that immersion? Could it be a twin element jobbie? Anyone know?)

Bendy_House

Arfa__ said:

Regarding the RC1 receiver, no sign anywhere of what connects to it. But in the big pile of manuals left to us by the previous owners, I found one for a T4RF thermostat which I suspect would have mated with that RC1. Also found a bunch of manuals for random other appliances not present in the house too! Including a Grundfos Home Booster pump...

Nice detective work

A quick Google confirms what you suspect - the WR1 was also used with that Drayton/BG T4RF. Astonishing that they left it wired up!

Er, what are your electrical DIY skills like...?

Ok, final mystery - where is the cylinder 'stat for the gas boiler? There MUST be something on there to tell the gas boiler to stop heating up the cylinder.

(It surely cannot be that pipe stat? Set to sense when the 'return' boiler water is so high that it's clear the cylinder cannae tak any mare, cap'n. If so, that's stupid-crude.)

Section62

Bendy_House said:

(Why are there TWO cables going to that immersion? Could it be a twin element jobbie? Anyone know?)

We'd need to check the instructions for Arfa__'s specific model, but based on previous experience the cylinder stat (for the boiler) is probably at the top of the space under that grey cover, so one of the cables (probably) is for the boiler wiring, the other one the immersion heater.

But I could be wrong, so the right instruction manual need checking.

If I am right, it is a good example of where one collection of (control system) terminals can be energised from more than one circuit... which means extreme caution is needed.

Bendy_House

Section62 said:

Bendy_House said:

(Why are there TWO cables going to that immersion? Could it be a twin element jobbie? Anyone know?)

We'd need to check the instructions for Arfa__'s specific model, but based on previous experience the cylinder stat (for the boiler) is probably at the top of the space under that grey cover, so one of the cables (probably) is for the boiler wiring, the other one the immersion heater.

But I could be wrong, so the right instruction manual need checking.

If I am right, it is a good example of where one collection of (control system) terminals can be energised from more than one circuit... which means extreme caution is needed.

Blimey - I didn't expect that!

Yup - as you say - page 20. https://mediacdn.heatraesadia.com/-/media/themes/heatrae/literature/discontinued-literature/megaflo-he-installation-manual.pdf?v=1&d=20170629T112101Z

Play with that TOP thermostat control, Arfa; it's the one that sets the cylinder water temp when it's heated by the gas boiler. Don't forget - it'll be a LOT hotter at the top of the cylinder than what's set there (not that it has an actual temp scale...).

What's your DHW temp like at the moment? Just nicely hot, or 'ouch'?

Arfa__

Bendy_House said:

Arfa__ said:

Regarding the RC1 receiver, no sign anywhere of what connects to it. But in the big pile of manuals left to us by the previous owners, I found one for a T4RF thermostat which I suspect would have mated with that RC1. Also found a bunch of manuals for random other appliances not present in the house too! Including a Grundfos Home Booster pump...

Nice detective work

A quick Google confirms what you suspect - the WR1 was also used with that Drayton/BG T4RF. Astonishing that they left it wired up!

Er, what are your electrical DIY skills like...?

Ok, final mystery - where is the cylinder 'stat for the gas boiler? There MUST be something on there to tell the gas boiler to stop heating up the cylinder.

(It surely cannot be that pipe stat? Set to sense when the 'return' boiler water is so high that it's clear the cylinder cannae tak any mare, cap'n. If so, that's stupid-crude.)

OK, so found the manual for this MegoFlo, the pages below seem most relevant (but let me know if you want more, e.g. wiring diagrams). Seems there is an indirect thermal cut-out behind that lower grey panel. The dial on the top bit there appears to let you control the temp it cuts out. This small black dial just goes from 1-5. I presume the flat side faces the selected number, which is currently just over 2.

@Bendy_House Is this the 'cylinder stat' you're looking for? (and as @kipsterno1 suspected)

The exact model of this Megaflo was in one of the earlier photos: CL300HE. The Manual covers models with immersion only and indirect models like this one. Wasn't immediately clear which we had, which was it was hooked up and isn't clear how the two systems are used concurrently.

As for the two cables, could one be for the immersion element and one for the indirect stat?

So, looks like the tank is being filled by the boiler. Good stuff, all on cheap(er) gas.

The redundant receiver - I'll get that removed when I next have an engineer out, not sure I want to fiddle with that myself.

What I'm not clear on, is how would heat from the immersion heater if I wanted to? Should it just be that one wall switch and manually turned on/off there? Or would there be another control system for it?

And if this is not the main electric usage, I guess I'm going to have to hunt around and check other stuff in the house now...

Bendy_House

Pffft - you didn't see my previous post - I beat you by 24 minutes. Thanks to S62.

That would seem to be it - under that cover is both the 'stat for the gas boiler, and the one for the immersion heater.

The black 1-5 control seems good to me if it's at '2'. I'd suggest you want the DHW temp to be just what you need for good showers and washing your dishes, and no more; not ouch hot so you always have to cool it down in the sink with lots of cold water, but still hot enough to give satisfying showers and/or baths. That's your call, but the cooler you have that cylinder set, the (slightly) more energy you'll save. That's because thermal dynamics says that the larger the difference in temps between two bodies - the cylinder water and the house temp - the more heat will transfer. Simple as that.

And then programme your Hive to provide this hot water for just when you need it. No point leaving a tank full of steaming water sitting there all day until you come home again; yes, it'll still be 'hot', but you will have lost more of that heat because the tank insulation ain't perfect - so that's waste.

Yes, the immersion will almost certainly be that manual switch - turn it on for heat, and off when it's hot. The 'stat - the red one - will prevent it from becoming too hot - it'll turn the element off when the chosen temp is reached. And it'll come back on again if the temp drops.

You might be able to hear whether the element is working - switch it on, make sure the cylinder water is cooler than the thermostat setting (so it's 'on'), and listen for a couple of minutes for a hiss or sizzle, just like a kettle being heated.It might be too faint, tho'.

Or, wait until the water is cool, turn on the immersion for 30 minutes, and try the water again...

It's worth having a working immersion just in case the boiler packs in and takes a few days to fix

Arfa__

Water temp is fine as it is, good for a shower, washing up etc without scolding. But still good to know where it can be tweaked.

I've tweaked the hive schedule, reduced it a bit to 1hr in morning, and 30 min in evening. So far, that's covering us.

I'll get that immersion heater checked at the next service (along with the redundant RC1), as you say, be good to have a backup option. Not heard it kick in at all, no light etc.

Many thanks for the help, it's definitely clearer how it all works now. Much appreciated.

Bendy_House

You're welcome.

That all sounds good.

I suspect the RC1 has been disconnected from its 'control' side within that wiring centre, when the new Hive receiver was added - one of the Hive's wires would have gone in its place. But why they then kept it powered up?! Lawdie.

I wouldn't worry about it - but it's daft to keep it.

I'd also ask the sparky if that pipe stat (at the very top above the boiler) is doing anything, and if almost certainly 'non', you might want that removed too - it just causes confusion.

Section62

Bendy_House said:

 

I'd also ask the sparky if that pipe stat (at the very top above the boiler) is doing anything, and if almost certainly 'non', you might want that removed too - it just causes confusion.

Not sure if you missed the posts saying it is very likely the pipe stat works in conjunction with the frost stat, so the central heating doesn't run continuously while the ambient temperature of the garage is below 5C?

A heating engineer would be a better person to ask though if necessary.  An electrician is more likely to shrug, or just do as instructed and remove it regardless of consequences.

Arfa__'s system is more complicated than most, not everyone will understand what the different components are for (or where they are) so it would be risky to ask an average electrician fiddle around with it.

Bendy_House

Yup, forgotten that reference.

And 'sparky' was a misnomer - I meant for the GasSafe to have a look when Arfa has the next boiler service. If the GS starts to suck in air through their teeth, then perhaps leave it...