Your chance to laugh and point: Combi bashers unite!!

[Leighloz]

I’m planning to get Bessie (the current boiler, 22 years old, a Gloworm fuel saver mark II with 15 kW of throbbing power!) replaced with a combi

I know you won’t want to miss this chance to tell me:
+ how terrible combi’s are and that it won’t work,
+ what I’ve forgotten,
+ that this or that brand is ace (or p a n t s)!
bet you can think of loads more…

Why scrap the old girl? Partly to free up some space and partly to improve the shower/ lower the gas bills/ hug more trees (and ‘cause I like risk! )

So if you would gentlemen (and ladies?)

What won’t work?
What do I need to remind the installer about?
How do I avoid adding to the 28000 other posts with “combi” in them?

Maybe I should share…

Installer recommends a Worcester-Bosch 30 CDi. HW 12.3 l/min@DeltaT:35 C, or 11.5 l/min@DeltaT:40 C - CH loads of headroom.
The 37CDi as an alternative looks like overkill (and over££££).

Where?

• Mid-terraced Victorian house. Moderately insulated. Leicester: hard water.
  1 bathroom. 1 kitchen. 2 beds. 6 rads All with TRV’s. Half are new type 22’s, half are old pressed steel (bulges likely to appear!).
  Mum, dad and 2 toddlers using the water/heating (so need variable temperature on HW to avoid bandaging scalded little hands).
  Plan to site in bathroom airing cupboard: it physically fits, there’s leccy, external wall for flue and access to external drain. Bye bye cold water tank, CH header tank in loft, vented HW cylinder, wired thermostat, (oh.. and apparently reliable hot water and CH, any redundancy, etc).
  22 mm gas pipe on outside wall to supply it. 3.5 m from gas meter.
  Gas supply also serves gas fire and gas cooker.

For when it breaks:

• Gas fire in front room.
  10.8 kW shower in bathroom.
  Deep pockets.

Stopping it breaking:

• I’m already on first name terms with the installer.
  Magnaclean will be fitted.
  Descaler was mentioned, but if an electric jobby will get some of the supplied snake oil and use that to lube the pipes before replacing it with polyphosphate device.
  Regular prayers to the heating gods and sacrificial offerings planned (see above reference to children ).

Pressures:

Static mains pressure: 2.4 bar (measured using £11 screwfix gauge from monument).

Maintained pressure @ flows (using a bucket, set of scales and a watch):

• Max flow: 22 l/min@ 0 bar (pressure drops to zero on outside tap when all other cold taps on – total volume calculated with a couple of buckets!!!)
  18 l/[email protected] bar (my kitchen tap)
  14 l/[email protected] bar (important this one as boiler only gives stated HW flow at 1.4 bar!)

Temperatures
Ambient mains water temp: 5 to 8 C (January!!!!)
The current bath hot tap (from vented cylinder) delivers 9 l/min.
The current electric shower delivers 4.7 l/min from the cold main @ outlet temp 43 C (will leave in and add a thermostatic mixer at some point so need fully modulating)...

 

[eyebrows]

I had a 30si in my last house and i couldn't fault it. It saved alot of space as the back boiler was removed and the flow rate was pretty good.

The house im in now i plan to keep my open vented system and have a 15Ri or if i go for overkill a 24Ri
That way any problems and the immersion keeps my bath warm The boiler is already in the kitchen so only taking the space of a cuboard and the way my airing cuboard is if i removed the cylinder it would be dead space anyway. But its an alternative just to make your decision abit harder

 

[Hugh Jaleak]

There can be an issue with old pipework, you are converting from an open system to a pressurised system, any leaks will soon manifest themselves! May be worth changing the old rads at same time IMO.

I prefer an immersion for backup, but you have the fire and a decent shower so can keep warm and clean if the worst happens!

 

[sloppytom]

the 30 maybe bit too big, maybe a 28 or 24junior would do, alot smaller, still give good flow rates and bout 200 cheaper

 

[Agile]

As you have given some dynamic flow rates it seems the matter is pretty much under control.

We would be charging about £2000 for that job.

The only comment I would make is that you should not be needing to remind a competent installer anything as long as he has explained the combi supplies just ONE hot outlet at a time.

Any other water usage can affect HW flow rate ( thats including WMC, dishwasher, garden hose, WCs etc.

Tony

 

[BingoBongo]

looks like you have mst areas covered

as above think about new rads and valves

forget the junior as you cant adjust hw temp


just go for it and post the pics so we can slaughter the guy..

 

[Registered Gas Man]

CDI is streets ahead of junior/si if you can afford the extra get a CDI.

 

[Agile]

Thats one point on which I could criticise him.

He has just given you the price for the cheapest boiler from that maker.

He should have offered you several models ( and other makes as well ).

Tony

 

[kevindgas]

as said the junior is an inferior boiler to the cdi
30 kw is about right don't get a 24 Kw as water production is average at best a 28 would be minimum i would recommend

worcester are a good manufacturer on the whole
the pipework may be an issue as previously said but i install loads and the old pipework has only failed on 2 occassions in 10 years.

 

[Leighloz]

Hi All,

As promised here are the pics. It all works fine. Flow rate in the bath is greater than with my old gravity feed - only disadvantage is the 30 sec wait for hot at the kitchen tap and that the leccy shower is prone to scalding or freezing if anyone touches another tap/flushes. Will get a thermostatic mixer shower soon.

Boiler:

Untitled

• Leighloz
• 19 Aug 2010
• 1

Shower feed:

Untitled

• Leighloz
• 19 Aug 2010
• 1

CH pipes to loft:

Untitled

• Leighloz
• 19 Aug 2010
• 1

Magnatec and Combimate:

Untitled

• Leighloz
• 19 Aug 2010
• 1

The install went fine (ok they looked to the sky a few times when I kept asking for neat pipework in the cupboard!), but getting the combimate fitted took a further 3 months and two engineers (neither of whom had ever seen one). Not all bad though as I didn't get charged for it in the end as a "sorry".

His quote looked cheaper than the others. A good price and I was happy to pay less and do the pipe clips and supplementary bonding - it seems they don't come as standard.....

Notes:
Winner: £2317 (guarantee 6 years)
Company 2 quoted £2790 (guarantee 6 years)
Company 3 quoted £2520 (guarantee 6 years)
Company 4 quoted £2650 (guarantee 3 years)

Prices inc. VAT. - long guarantee due to being accredited installers.


If you want to know who he is, PM me and I'll tell you. Leicester based.

Leigh.

 

[doitall]

Given that it's always more difficult to alter an existing system, I would rate it 3/10 for neatness, and 1/10 if you had to clip the pipes.

Now who do I know in Leicester, that I've just upset.

 

[boilerdoktor]

the 30 maybe bit too big, maybe a 28 or 24junior would do, alot smaller, still give good flow rates and bout 200 cheaper

Difference between the 30si and 28i ponds wise is about £100. For that you get a temp control on the hot water which is usefull. Personally i'd go for the 30 cdi! 24i was only manufactured for flats and the like, wouldn't put it in a house ( 9 l per min on hot water)

 

[Servotech]

I don't want to alarm you but that wiring featured in pic2 and 3 which is wraped around the heating pipes is simply not safe and you need to move it ASAP.

 

[Razor900]

Given that it's always more difficult to alter an existing system, I would rate it 3/10 for neatness, and 1/10 if you had to clip the pipes.

Now who do I know in Leicester, that I've just upset.

J you're such a perfectionist

It's worth at least 2/10

Oops perhaps I live a bit to close to comment

 

[doitall]

Better make that 9/10 Ray just in case.