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eldar

Original Poster:

8,335 posts

81 months

[news] 
Tuesday 22nd June 2010 quote quote all
I'm having my combi boiler replaced. Plumber has recommended a megaflow system, with a new boiler and a hot water tank, which should improve hot water (2 bathrooms, miserable hot water in winter).

Suggests a Baxi megflow 28 HE boiler and a Baxi S 170l tank. As the existing boiler is a baxi, and as reliable as a 1972 lada, I'm hot convinced a new system will be any better. Am I being paranoid, or have they improved?

The estimate is £2,500, inc. VAT, is this reasonable?

Ferg

15,242 posts

142 months

[news] 
Tuesday 22nd June 2010 quote quote all
Depends what pipework is there already.

What I always bang on about on these threads is that you MUST have enough flow to run an unvented cylinder. I wouldn't consider installing one on less than 25 litres a minute and with less than 3Bar coming in.

B17NNS

12,670 posts

132 months

[news] 
Tuesday 22nd June 2010 quote quote all
Price sounds good.

If you have reliability concerns over his choice of boiler ask him to cost up an alternative.

A Bosch system will be more expensive but their boilers come with a five year warranty and may be more efficient.

I have a Baxi combi. No issues other than regular servicing since it was installed 4 years ago.

Skyedriver

5,082 posts

167 months

[news] 
Tuesday 22nd June 2010 quote quote all
Been talking to a plumber chap this evening about the possibility of replacing the old oil combi (and tank) (yes still haven't decided the preferred heating route). Can anyone explain the difference between vented and unvented tanks - he was recommending a Magaflow too.
Also spoke to a guy doing PV panels - get money back from the electric co. but £10k to install! & wood pellet stoves - less expensive but needs room space, cheaper running costs apparently 5p/kw

Ferg

15,242 posts

142 months

[news] 
Wednesday 23rd June 2010 quote quote all
Skyedriver said:
Can anyone explain the difference between vented and unvented tanks
Vented cylinders are fed from a storage tank above and vent via a vent-pipe up and over into this tank. Pressure at all outlets relies on gravity or pumps.

Unvented cylinders are fed from the mains cold in the house. They allow for the expansion either with an expansion vessel taking the expanding water from the system and allowing it to compress air via a rubber bag/diaphragm. Unvented cylinders run at around 3Bar these days (NOT mains pressure, unless the mains is this low).
The BIG drawback with Unvented cylinders is that as soon as you run a bath, for example, you are opening two 3/4" (maybe) valves (hot &cold) and ALL the water that's coming out is effectively coming down the main from the street. In many properties this can be 15mm.... Flow-rate is CRITICAL. You CAN'T overcome poor flow with pressure to any useful extent). You can STORE water at pressure within the building and this can help, but it's expensive.

Be aware that in many situations VENTED cylinders are still the best bet.
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JohnRS4

277 posts

131 months

[news] 
Wednesday 23rd June 2010 quote quote all
I'm about to have a Megaflo installed, Heatrae Sadia 30CDI, and on recommendation of the plumber having the pipe from the main to the house increased to 32mm.

SJobson

8,648 posts

149 months

[news] 
Wednesday 23rd June 2010 quote quote all
Ferg is absolutely right. I had a megaflo-type unvented cylinder installed at my old house, and the limiting factor was the fairly small-bore pipe coming from the main; it was obvious that plenty of houses down the street had had that replaced, and I was intending to do so when the drive was resurfaced, had I stayed there.

The other thing to be aware of is that obviously with a decent flow rate, they empty quite quickly so get as big a capacity cylinder as you can fit.

ln1234

848 posts

83 months

[news] 
Wednesday 23rd June 2010 quote quote all
Ferg said:
Skyedriver said:
Can anyone explain the difference between vented and unvented tanks
Vented cylinders are fed from a storage tank above and vent via a vent-pipe up and over into this tank. Pressure at all outlets relies on gravity or pumps.

Unvented cylinders are fed from the mains cold in the house. They allow for the expansion either with an expansion vessel taking the expanding water from the system and allowing it to compress air via a rubber bag/diaphragm. Unvented cylinders run at around 3Bar these days (NOT mains pressure, unless the mains is this low).
The BIG drawback with Unvented cylinders is that as soon as you run a bath, for example, you are opening two 3/4" (maybe) valves (hot &cold) and ALL the water that's coming out is effectively coming down the main from the street. In many properties this can be 15mm.... Flow-rate is CRITICAL. You CAN'T overcome poor flow with pressure to any useful extent). You can STORE water at pressure within the building and this can help, but it's expensive.

Be aware that in many situations VENTED cylinders are still the best bet.
If you do go for an unvented system and don't have flowrates to match, something like this would work quite well. It's about the size of a fridge and costs around £1500.

Ferg

15,242 posts

142 months

[news] 
Wednesday 23rd June 2010 quote quote all
I'm not sure that's particularly cost effective and I notice they don't promise improved flow rates either!!
I'd favour an accumulator. Bigger, but less money, much simpler plumbing and no pump to go wrong.

Grandad Gaz

3,907 posts

131 months

[news] 
Wednesday 23rd June 2010 quote quote all
Ferg said:
I'm not sure that's particularly cost effective and I notice they don't promise improved flow rates either!!
I'd favour an accumulator. Bigger, but less money, much simpler plumbing and no pump to go wrong.
I'm going for this system. Equal pressure to both hot and cold!

http://www.gah.co.uk/heating/dualstream/why-choose...

Ferg, Fakenham too far for you to work? smile

V10Mike

421 posts

91 months

[news] 
Wednesday 23rd June 2010 quote quote all
Grandad Gaz said:
Ferg said:
I'm not sure that's particularly cost effective and I notice they don't promise improved flow rates either!!
I'd favour an accumulator. Bigger, but less money, much simpler plumbing and no pump to go wrong.
I'm going for this system. Equal pressure to both hot and cold!

http://www.gah.co.uk/heating/dualstream/why-choose...

Ferg, Fakenham too far for you to work? smile
That's the system we've got, with two 300 litre cold water accumulators. Runs two bathrooms and three showers, and all can go at the same time! We started with one 300 litre tank but it wasn't enough. Now it's fantastic.

mk1fan

4,657 posts

110 months

[news] 
Wednesday 23rd June 2010 quote quote all
Ferg,

Any chance you could PM me your company details. I think that you may be of use to me!!

Hereward

1,618 posts

115 months

[news] 
Thursday 24th June 2010 quote quote all
Ferg said:
Depends what pipework is there already.

What I always bang on about on these threads is that you MUST have enough flow to run an unvented cylinder. I wouldn't consider installing one on less than 25 litres a minute and with less than 3Bar coming in.
Indeed. If the heating engineer didn't check flow and pressure then he's not the right man for the job.

andy43

3,546 posts

139 months

[news] 
Thursday 24th June 2010 quote quote all
GAH is pricey - we've done a similar thing with an expansion vessel and it works great eg 300 litre vessel for under £350 and then add your unvented cylinder of choice.

eldar

Original Poster:

8,335 posts

81 months

[news] 
Thursday 24th June 2010 quote quote all
Hereward said:
Ferg said:
Depends what pipework is there already.

What I always bang on about on these threads is that you MUST have enough flow to run an unvented cylinder. I wouldn't consider installing one on less than 25 litres a minute and with less than 3Bar coming in.
Indeed. If the heating engineer didn't check flow and pressure then he's not the right man for the job.
The plumber did check pressure and flow, 3 bar and 17 l/min. Low flow, but explained by the 22mm incoming main being 'throttled down' by 15mm piping to the taps. He would replace the 15mm with 22 from the main to the tank. Sound reasonable?

Ferg

15,242 posts

142 months

[news] 
Thursday 24th June 2010 quote quote all
eldar said:
Hereward said:
Ferg said:
Depends what pipework is there already.

What I always bang on about on these threads is that you MUST have enough flow to run an unvented cylinder. I wouldn't consider installing one on less than 25 litres a minute and with less than 3Bar coming in.
Indeed. If the heating engineer didn't check flow and pressure then he's not the right man for the job.
The plumber did check pressure and flow, 3 bar and 17 l/min. Low flow, but explained by the 22mm incoming main being 'throttled down' by 15mm piping to the taps. He would replace the 15mm with 22 from the main to the tank. Sound reasonable?
Ask him if he can guarantee that you will be able to turn all the hot and cold outlets on without a loss of flow anywhere.

allgonepetetong

1,171 posts

104 months

[news] 
Wednesday 30th June 2010 quote quote all
Ferg said:
eldar said:
Hereward said:
Ferg said:
Depends what pipework is there already.

What I always bang on about on these threads is that you MUST have enough flow to run an unvented cylinder. I wouldn't consider installing one on less than 25 litres a minute and with less than 3Bar coming in.
Indeed. If the heating engineer didn't check flow and pressure then he's not the right man for the job.
The plumber did check pressure and flow, 3 bar and 17 l/min. Low flow, but explained by the 22mm incoming main being 'throttled down' by 15mm piping to the taps. He would replace the 15mm with 22 from the main to the tank. Sound reasonable?
Ask him if he can guarantee that you will be able to turn all the hot and cold outlets on without a loss of flow anywhere.
And if he can't?

I'm following this thread carefully as I am also considering a change of system.

I have a megaflow in my new build flat, 2 bed 2 bathroom, and think it is fantastic - obvously there is a large bore mains feed. I need a system in my 3 bed 1930s house that can accomodate running a shower, washing machine and kitchen tap, toilet flush etc simultaneously. CurrentlI have an old combi and electric shower. If one is in the shower, others can't flush the toilet without the flow being affected and scorching one's back.

This is a problem that needs fixing!

Edited by allgonepetetong on Wednesday 30th June 09:59

Ferg

15,242 posts

142 months

[news] 
Wednesday 30th June 2010 quote quote all
If he can't.....

Think very carefully about whether you want to spend a lot of money and then compromise.

If you have a poor mains feed then the first call would be to the water authority. Ask them if they can upgrade it and how much it would cost.

If you have PRESSURE, but not flow then maybe an accumulator is the way forward.

allgonepetetong

1,171 posts

104 months

[news] 
Thursday 1st July 2010 quote quote all
Can flow be acquired by fitting a large bore mains feed if pressure is present?

Ferg

15,242 posts

142 months

[news] 
Thursday 1st July 2010 quote quote all
allgonepetetong said:
Can flow be acquired by fitting a large bore mains feed if pressure is present?
Depends on the flow available in the road. You need a minimum of 25mm to the house really, although a lot will depend on the length, obviously.
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