Want a megaflow - can my old oil heater be a primary heat source?

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Folks,

I have a 22 year old oil boiler supplying CH and HW. I will be installing a large pv solar setup and I want to use excess to heat water. I was eyeing a 200L megaflow.

Can the old, perfectly functional boiler, be used as primary or do I need to increase budget by £7.5k in budget :(


C
C
 
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If it currently serves an indirect cylinder for hot water, there would appear to be no reason why not.
 
Which boiler do you have ?
Valid point. See attached
IMG_20220406_112847__01.jpg


If it currently serves an indirect cylinder for hot water, there would appear to be no reason why not.

No, it's direct (is that a thing?).
I seems to have a small hot water store because I can run the hot tap for a few seconds and get hot water before it fires.
 
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1. You can use the existing combi boiler to heat the coil in an unvented cylinder. You will need to:
1a. Convert the existing radiator circuit into two zones with either a 3 way motorised valve or two x 2 way motorised valves. I'd opt for two 2 way valves, as if you go for the 3 way you would need another 2 way for the unvented cylinder in addition.
1b. Install a programmer to control the heating / hot water times.
1c. Possibly install an automatic bypass to cope with the situation where all radiator valves are closed. May already be one in boiler.
2. Connect the PV output two the two immersion heaters in the unvented cylinder.
3. Make sure the thermostats on these heaters are set a few degrees (2 or 3 degrees, but they aren't very accurate) higher than the indirect heating coil thermostat.
 
thanks.

From an electrical side of things, I'm ok. I can control the PV invertor to turn on a relay/contactor when the batteries are at 80% (or whatever I want).

From memory, it was a while ago when I replaced the thermostat circuit with a smart system (evohome), I remeber seeing a bridge on the HW sense terminals. I will check again. I was thinking, I could use a timer to make toggle with the batteries. That way, if the HW cylinder is not up to temp then the oil will sort it out.

The part I am unsure of is the plumbing. @oldbuffer - I think you're saying divert the CH circuit into the cylinder or not into the cylinder and control that flow?
If so, then the original HW side of the boiler will never be used as it will always be CH?


C
 
the original HW side of the boiler will never be used
Correct.

It's just using the boiler as a heat only, exactly the same as any other system with a hot water cylinder.
It either heats the cylinder, radiators, or both.

You could have one HW outlet near the boiler heated by the HW part of it if you wanted, which would save water if the cylinder was far away.
 
exactly the same as any other system with a hot water cylinder.
thanks. That makes sense with what I am seeing on the interweb. :)

For simplicity, it makes sense to leave the kitchen tap on the boiler (it's located under the counter). The main users of HW are all upstairs - 3 bathrooms. I could put the cylinder in the loft (above the bathrooms). Benfits are many - HW is closer to all consumers.
Only complication would be to run another pipe from boiler to cylinder. I assume the return can just be found on the closest rad return? I don't need to run a seperate return.
 
1. In response to post #7.
1a. An unvented cylinder requires a two port motorised valve controlled by the thermostat in the cylinder to open / close the flow of hot water from the boiler to the internal cylinder coil.
1b. A 3 port, mid-position valve cannot be used as it won't necessarily close the hot water side of the circuit.
1c. A 3 port diverter valve could in theory be used, although in my view is isn't as good as using separate 2 port valves, one for heating, one for hot water.
1d. Whatever valve is used for the unvented cylinder, it cannot be a "Motor On, Motor Off" (MOMO) valve, it must be a spring return valve as these fail safe.
2. Using the existing combi DHW for the kitchen is an excellent idea. Much shorter pipe runs, and less "water gone cold" to waste.
3. You would need an additional return pipe. The hot water cylinder return to the boiler must be the last tee on the return pipe, or you can get reverses circulation, with radiators heating when only water heating is called for.
 
thanks. That makes a lot of sense.
For clarity, I am doing research because a) I want to understand if it's possible with my existing setup b) I like to understand how these things work but will be getting a local plumber to do the work. :)
 
I like to understand how these things work but will be getting a local plumber to do the work
Based on this, what should I be looking for in a local plumber or is this a standard setup?
I've litrally thrown money down the drain in the past because I got a "generic" guy when I had actually needed a drainage specilist. Don't want to make the same mistake again.
 
1. For the unvented cylinder, the installer must be "G3" registered with an accreditation organisation. Gas Safe can accredit, as can NAPIT and a number of others.
2. Installation of an unvented cylinder must be notified to your local Building Control department. The necessary certification and notification can be done by the installer provide he / she is currently accredited by an appropriate "competent persons" scheme
3. I can't help on the electrical side - don't know enough about it.
 
I picked-up that you'll be using the PV to charge a battery pack, but that you would use a relay to switch to the immersions once the batteries are x% charged. This seems a little primitive - remember that the battery pack may not take all of your PV output when charging (it's a LARGE array, right?).
Better, IMO, is to feed the immersion heaters via a dedicated PV diverter such as Solar iBoost or Immersun. That way you would use excess PV power even when the batteries are charging.

As said by others, you should run a dedicated return pipe from the new cylinder to as near to the boiler return connection as practicable.

Literally...adverb version of literal
Specialist...having a special quality or attribute.

If Cockneys (and Yorkies) could speak properly they'd stand a better chance of spelling correctly.:sneaky:
 
Thanks @oldbuffer

@MeldrewsMate
Yes, it's a rather blunt way of doing / describing it. I've seen those options you're referring to and will look more into those.
The arrary I am installing is a 6KW PV with a 5KVA invertor. (Overspecced the arrary to improve winter capture). My house "idles" at around 500W when we're home so there should be lots of time for the HW if done correctly like you mentioned.
 

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