Megaflow or Combi???????

[manwithmission]

Hi

Which is the best route to take, a Megaflow HE or Combi Boiler?

We’re in a 4-bed house, 2 kids, bathroom & en-suite (2 showers, one bath).

We have a traditional gravity-fed boiler & tank set-up, which came when the house was built 12 years ago. The shower used to be OK (not as powerful as we would like, but OK), now it varies in pressure & seams to constantly get air locks. It’s really sensitive to the height setting. The higher the shower, the weaker the flow. I have to place the shower in the tray to allow the air locks to blow though. It’s a real pain.

We were thinking about changing the boiler this year & had been told that Combis are the way to go, but it’s now been suggested that we keep the boiler & go for a Megaflow HE????

Which will give the best Shower Pressure?

Which is the most Efficient method?

How many years before a Boiler should be changed? Do they become inefficient after a certain age?

If we changed our Boiler, would the Megaflow become redundant?



Thanks for any advice!

 

[corgiman]

Whoa

dont try a combi on a place that has a high demand like yours, steer well clear, as the more taps you open the less water comes out.

megaflow is the way to go

 

[ollski]

God yes, go with the megaflow. You can always replace the boiler later if needs be and leave the rest of the system intact. Not all boilers are capable of being fitted to a pressurized system though....which boiler have you got?

 

[kevplumb]

you can open vent some pressurised cylinders

 

[manwithmission]

Thanks guys.

Boiler is an "Stelrad/Ideal Elan 2". It's 12 years old & I've extended the house substantially last year.

 

[corgiman]

well if you are updating the hot water system, why not update the boiler as well

if not it will be ok to pop a megaflow on that

 

[noonespecial]

But have you got adequate water flow rate and dynamic water pressure for a Megaflo? You need to get that checked first. You would also need that checked for a combi but they do not demand as high a requirement as unvented cylinders.

You probably have a 15mm incoming water supply that may not be adequate to feed a bath and a good shower at the same time.

You need to get someone who is trained and registered for installing unvented systems - contact Institute of Plumbing and Heating Engineers Association of Heating and Plumbing Contactors, etc for suitably trained people. Statistics show that unvented systems are safer than traditional open vented systems if they are installed correctly. If they are not they can explode with severe force as MacDonalds and others have found out

Do not attempt to install an unvented cylinder yourself

 

[Handyman]

Definitely not a combi - especially in a house/family the size of yours. Who told you "Combis were the way to go", and why? Go for Megaflow - or a Megaflow type system. I've gone for a Range Tribune cylinder. Excellent quality, and good value deals available from P***b**e, and it comes with all the bits you need including the expansion vessel. See thread on this forum dated 5th Feb for pressure/flow information. (I don't know how to provide direct link, so you'll have to look)

 

[manwithmission]

I’m definitely NOT going to attempt this myself!

I’ve been quoted £1300 to supply & install the Megaflow CL170HE.

I don’t understand what is meant by “vented / unvented”, but I know this Megaflow has to have a vent pipe to the outside in case it blows.

We have 22mm Blue PE coming into the house, but then 15mm after the Stop-cock. Would replacing that with 22mm be of benefit?


What Boiler would you suggest & how much would that add to the bill?



Thanks again.

 

[ACOperson]

Yes, the water pressure AND flow rate have to be checked. The size of the incoming main is important but I know someone who has had an unvented for about 4 years on a 15mm main, but the pressure and flow rate are just enough to feed it.

An unvented system is definitely the way to go for your size property, providing the water supply is up to it. With a combi, only so much water can pass through the plate heat exchanger, so the minute someone runs a bath while you are having a shower, you will suddenly get very cold! With an unvented system, all the water in the cylinder is already at the correct temperature, so you can open multiple draw off's and they will all be at a correct, uniform temperature.

The unvented cylinders lose very little heat as their insulation is excellent, and if you buy one with a good coil (22kw +) they will reheat just as fast as you are using the water!

Get a professional (heating engineer, not your builder) to come and have a look. The only drawback to unvented is that you will still have a sodding great cylinder in the cupboard!

 

[noonespecial]

The vent pipe is not a vent pipe - it is a safety pressure relief valve / expansion valve tundish discharge.

With an unvented cylinder you do away with the cold water storage cistern which feeds a 'traditional ' vented system and the safety open vent pipe. The domestic hot water system then becomes sealed or unvented and is for your purposes fed from the incoming cold water main.

For your purposes all hot and cold water would be fed off the incoming cold water main.

Does the blue poly PE pipe have a 22mm (3/4") INTERNAL bore? How have you determined that?

Why are you thinking of changing your boiler? Does it work? It may have a few more years life in it yet.

 

[Handyman]

You don't specify the size of cylinder. I would suggest about 210litre cylinder to cope with your demands - especially if your kids are in their teens and start to get hang-ups about showering all the time.

I've just ordered a 180litre Range Tribune: £572 incl. Vat (supply only) from P***b**e. You'll have to get a plumber to fit it, of course - and one who has experience and knowledge about fitting sealed systems, and probably not the bloke who told you "Combis were the way to go" who, possibly, doesn't have the requisite knowledge.

Vented means that there is a pipe leading up into the loft which points down over your header tank. If/when any pressure builds up (when the water gets hot or overheats), it vents over the tank, and any excess water just goes into the tank. Unvented means that there isn't a vent pipe, but the excess pressure is taken up by an expansion vessel which has a pressurised rubber membrane in it which expands and contracts with the water pressure. Unvented systems also have a safety valve which operates if all else fails, and this has to have a pipe to the outside to eject boiling water and steam safely.

If you've got a 22mm mains supply pipe, then definitely change the stopcock and pipe to 22mm (that's if it's practical to replace the pipe, of course). That way you will ensure maximum flow is available for your Megaflow (or whatever), and the additional cost would be minimal.

 

[ACOperson]

If your mains pipe is 22mm internal diameter then you would do well to increase that to 22mm to the cylinder, and balanced cold draw offs, THEN reduce it to 15mm to taps etc.

Regarding the boiler, yes it may have a few years left in it, however if you do have the funds available then you may be better updating it to a model which automatically modulates, that way it will be running most efficiently when CH, DHW or both are on. With boilers which are range rated or pre-set to a particular output, you often have a situation where they work perfectly on DHW call, but are then far too high when CH only is on, so they cycle on and off.

£1300 is a very decent price to supply and install that cylinder, is that from a CORGI engineer who is qualified to install these? The unit itself is about £850, so that price is very cheap. Beware of dodgy installers, they will at best invalidate any guarantees, and in extreme worst cases endanger life and property!

Oh yes, I agree with the post above, a 210 at least is more like what you need.

 

[noonespecial]

The only drawback to unvented is that you will still have a sodding great cylinder in the cupboard!

Yes but it keeps the cupboard at just the right tempertaure if you brew your own

 

[corgiman]

just remember that you dont have to be CORGI'd up to install unvented, just proven competent

dont forget to inform the local building office like what we all do when popping in unventeds