Replacement UV cylinder

[fezster]

As the kids are growing, I'm finding our 250L Megaflo is occasionally running out of HW.

What are opinions on having a second UV cylinder vs having a bigger 400/500L cylinder fitted? Any pros and cons?

My Megaflo is "only" 7 years old. Is there any resale value to these things, or do I just have to have it gotten rid of?

And in terms of brand - seems the Joule is recommended. Any others to consider? As I already have all of the fitting kit (PRV, SRV, 2 Port Valve etc) - I assume a qualified G3 installer will be happy to just replace the cylinder, or would they rather replace everything? What would the pro installers here do?

 

[JohnD]

How is the cylinder heated? How long does it take to heat from cold?

How long are the showers they take?

How big are your shower heads?

 

[muggles]

250L of stored hot water is about 400L at showering temperature, and that's without taking into account any heating being provided by your boiler while it's being used. Maybe what you actually need is flow restrictors on the showers?

You can't re-use the existing control valves with a new cylinder. The new ones are supplied with the cylinder and must be used if you want your warranty to be valid, and your installation to comply with Building Regs

 

[fezster]

How is the cylinder heated? How long does it take to heat from cold?

How long are the showers they take?

How big are your shower heads?

Indirect cylinder. Recovery time is about 30 mins.

Showers are around 20L/min. Maximum two being used at any one time. I know Megaflos lose some capacity because of the internal baffle. so I'd expect to get just over 12 mins of usage if running continuously. I do have the cylinder being heated whilst in use, but the problem is heating is on at that time as well, so I suspect the cylinder is not getting the flow temp it should be to fully heat up.

 

[fezster]

You can't re-use the existing control valves with a new cylinder. The new ones are supplied with the cylinder and must be used if you want your warranty to be valid, and your installation to comply with Building Regs

That's useful to know. I also noticed the Joule cylinder doesnt seem to be available without the fitting kit anyway.

 

[JohnD]

Buy some smaller shower heads.

 

[fezster]

How about second cylinder vs one larger cylinder? Pros and cons?

 

[DavidLewis]

Indirect cylinder. Recovery time is about 30 mins.
... I do have the cylinder being heated whilst in use, but the problem is heating is on at that time as well, so I suspect the cylinder is not getting the flow temp it should be to fully heat up.

Is your house badly insulated? If not, why not reconfigure your system to be hot water priority? That way, the whole of the boiler's power can go towards re-heating / maintaining the HW temperature (assuming the indirect coil is up to it). Also, with hot water priority, there's a chance your boiler may be able to operate in "dual temperature" mode, whereby its flow temperature goes up to maximum to heat the hot water as fast as possible.

 

[Nozzle]

My Megaflo is "only" 7 years old. Is there any resale value to these things, or do I just have to have it gotten rid of?

They're made from stainless steel which has a reasonable scrap value. Copper and Brass even more so. To unlock the value though, you need to separate the cylinder down into constituent parts, metal by metal. Don't take the cylinder along as a cylinder... the scrappy doesn't want to be paying for the weight of lime scale so you need to demonstrate your cylinder is a pile of metals, not a cylinder.

Nozzle

 

[cdbe]

I have a couple of waste water heat recovery systems which are basically heat exchanger waste pipes that use the warm shower water going down the drain to preheat the cold water going to the shower thus reducing demand for hot water. They are potentially difficult to retrofit and expensive to buy new (but then so is a big UV) but are free to run.

 

[fezster]

Is your house badly insulated? If not, why not reconfigure your system to be hot water priority? That way, the whole of the boiler's power can go towards re-heating / maintaining the HW temperature (assuming the indirect coil is up to it). Also, with hot water priority, there's a chance your boiler may be able to operate in "dual temperature" mode, whereby its flow temperature goes up to maximum to heat the hot water as fast as possible.

Thanks - good advice, and something I have considered. Alternatively, I may just configure my heating to go off around the time we wake up, as the house does not lose heat that quickly.

 

[Ryler]

Have a neighbour with a 300l unvented and one of his sons will stand under the shower until the cylinder is emptied.
Perhaps thats the problem you have.

 

[JohnD]

I stayed at a place in the Australian interior where each bathroom, and the kitchen, had its own small cylinder. The advantage was that no hog could drain the entire supply. They did not encourage water waste.

(they used solar heating, but the principle stands)

 

[phatboy]

If you only occasionally run out, can you boost using the electric element on those occasions?

Sounds like a massive tank already....!

 

[ScottishGasMan]

What model and size of boiler is heating the megaflow?

as far as 2 smaller vs 1 larger, theres pros and cons to both, in short if you were changing it, you want 1 larger one.

2 smaller ones will potentially have a higher recovery rate as 2 slightly smaller coils will more often have a higher heating capacity than the slightly larger one in a single big cylinder, but unless its a pretty massive boiler your never going to heat radiators and 2 seperate unvented loops at full speed anyway. To add megaflow baffles break down over time so buying a 2nd cylinder just now, as well as needing a lot more space/controls and pipework, will still end up needing to replace the megaflow sooner or later, so as well ditching it and fitting a bigger cylinder if your going down the route of spending cash on it.

Depending on boiler style you may have the option of upgrading controls to give priority hot water, ie, it will only heat rads or HW at any one time, doesnt sound good, but you rarely notice it when set up properly, boiler puts 100% power into cylinder, then once heated will switch back to radiators.

Depending on temperature your running cylinder at just now, it can also be an option to fit a blending valve on the outlet (mixes cold water with the hot) so that you can turn the temperaure of the cylinder up to maximum, say 70°c, blended to 50°c, your effectively storing more heat in the same volume, the blending valve will then draw hot from cylinder at a slower rate than you currently draw water off the cylinder and once mixed with the cold will bring the flow to the hot outlets back up. They used to use very small cylinders in small flats but heat them up to 80 odd degrees and have them blended down to give the same use as a notably larger cylinder.