Glow Worm Ultimate 60FF replacement

[M271]

I am looking to replace my 12 year old Glow worm 60FF with a condensing boiler in my 4 bedroom, 2 bathroom detached house.

The 60FF has a stated max heat output of 18kw. The total radiator output is calculated at 14kw (15 radiators), I've recently had cavity wall insulation fitted, the house is double glazed with good loft insulation, the current boiler has always managed to cope in the past with all but the most coldest weather and hopefully the wall insulation will improve this.

However I have had the following contradictory advice and i'm getting confused about the most appropriate replacement. Any advice/clarification would be appreciated from you knowlegeable bunch out there!!
I've had the following advice so far:-
Glow worm advice - direct replacement is 24HX Flexicom, same gas supply pipe diameter 15mm, heating flow/return 22mm, rear flue.
Local Installer 1 - 24HX will be too high an output and could cause a kettle sound in the 22mm output pipes, receommended 18HX same output as current boiler.
Local Installer 2 - Recommend Worcester Bosch Greenstar 24Ri, but will need to bore new flue or lower position of boiler (currently rear flue), install 22mm gas supply pipe.
British Gas (think of a price and double it !!) - Worcester Bosch Greenstar 24Ri, but will need additional work to convert to 22mm gas pipe, bore new flue and convert to 28mm fully pumped (6m head) ??

I have read that condensing boilers should be worked as close to full output as possible for maximum efficiency, is this true.

Any advice would be appreciated.

 

[chrishutt]

Condensing boilers are likely to be more efficient on part load rather than full load. However even the 18 kW boiler will be operating on part load almost all the time (except in the coldest weather) so I doubt whether it would make much difference. At very low loads (i.e. very mild weather) you'd expect a smaller boiler to be more efficient, but again not much in it.

With 2 bathrooms your hot water demand might be quite high and although it is usual to add 2 kW or so to cover that you may need to make a more generous allowance on top of the existing heating load if you want to avoid running low on hot water and/or heating capacity in very cold weather, depending on the capacity of the hot water cylinder.

The main reason for choosing the lower output boiler would be (a) price and (b) possibly avoiding need to upgrade the gas supply (don't assume that the existing gas supply is adequate for 18kW - it may well be undersized). However you must decide who's advice you want to take based on your assessment of their competence. For example which of them were able to explain the issues mentioned above adequately?

 

[gas4you]

I would go for the Vaillant Ecotec Plus 618 system boiler. This may need the gas pipe increased in size, but this is something only your local engineer can ascertain on site from his calculations.

The Vaillants can be range rated down upon commissioning, so it could be set for say 14Kw as you have had cavity insulation added and timed for dhw to come on 30 mins before the heating every morning so dhw cyl gets full boiler power to heat it quickly and then ch gets full boiler power.

First thing on a cold morning is likely to be the only time the boiler's full set output is needed.

 

[Denad]

The initial question included the fact that the Flexicom has a rear flue, like the 60FF. Does this mean that the Flexicom can use the old 60FF flue. If not, why not?

If the flue has to be replaced, it will cost me £500 for scaffolding - a cost I am anxious to avoid. If the old flue cannot be re-used then is there any way of removing and replacing it from indoors or of putting the new one through the old one?

And how do I find an agent for Glow Worm that will replace the boiler under the government free replacement scheme?

Glow Worm will not answer my query - sent several times.

 

[Piers1989]

A high efficiency boiler works through modulation. It controls the rate at which it runs based on temperature. See it like you're driving and have cruise control. It can maintain a certain speed effectively. The same applies for the boiler.
In reply to the comments about choosing Vaillant over the flexicom, the flexicom software also allows you to range rate the appliance so this doesn't have any advantage from one make to another.
The size of the gas pipe does not rely on what make of boiler it is. It's all down to how much gas it can supply to an appliance. This should be calculated by an engineer based on the usage of gas on that particular run and current gas regulations.
About the flue, quite simply no. You cannot use the same flue. They are made from different materials and the flues are boiler specific. It's important to use the right flue for your own safety and regulations of course.

 

[misterdubya]

Seeing as this topic was posted 7 years ago, I suspect the OP has sorted out the situation by now.

 

[Denad]

Thanks Piers,

The Flexicom has connections to facilitate the direct replacement for a 60FF (per Glow Worm). The rear flue seemingly at least facilitates the same path through the wall as that for the 60FF. Can this be undertaken, in any way, from indoors to save the £500 scaffolding bill? I can't understand why the flue material matters - if it is good enough for one then surely also the other.

Also, how can I find an installer, under the free scheme, who is an agent for Glow Worm. All those that I have contacted are not and they will not recommend anybody else - and Glow Worm will not advise.

 

[Tibbot]

I can't understand why the flue material matters - if it is good enough for one then surely also the other.

What qualifies you to say 'surely'? By that do you mean you're SURE you should be able to use an old, incompatible, non-fitting flue on a new boiler?

How do you propose to secure and combustion seal and old flue to a new, different type boiler? What temperatures do you think the exhaust gasses will be compared to the old boiler and what effect do you think that would have on the old flue material?

Your question has already been answered, yet you persist with the same inane comment. Driven no doubt only by a desire to penny pinch even at the expense of your own safety.

 

[Piers1989]

Thanks Piers,

The Flexicom has connections to facilitate the direct replacement for a 60FF (per Glow Worm). The rear flue seemingly at least facilitates the same path through the wall as that for the 60FF. Can this be undertaken, in any way, from indoors to save the £500 scaffolding bill? I can't understand why the flue material matters - if it is good enough for one then surely also the other.

Also, how can I find an installer, under the free scheme, who is an agent for Glow Worm. All those that I have contacted are not and they will not recommend anybody else - and Glow Worm will not advise.

You're welcome... sorry i hadnt noticed it was posted such a long time ago!
The flexicom is the nearest replacement for the ultimate. The flue can take the same route but it would have to be the specific flue for the appliance. They operate at different temperatures (on the flue gas side of it) so the ultimate one is not safe to use with the flexicom. You can get the flue attached to the back of the boiler and then fed through the wall but then it would need to be sealed correctly so i think you would need access to the outside. The installer would be the best person to ask after they have had a look at the situation. Its hard to be certain without seeing what you have. If you see where im coming from...
I think there is some information on the Glow Wom website for installers...

http://www.glow-worm.co.uk/

on the right of the page it has a section about finding an installer. Follow that and it should point you in the right direction.

Piers

 

[Piers1989]

I can't understand why the flue material matters - if it is good enough for one then surely also the other.

What qualifies you to say 'surely'? By that do you mean you're SURE you should be able to use an old, incompatible, non-fitting flue on a new boiler?

How do you propose to secure and combustion seal and old flue to a new, different type boiler? What temperatures do you think the exhaust gasses will be compared to the old boiler and what effect do you think that would have on the old flue material?

Your question has already been answered, yet you persist with the same inane comment. Driven no doubt only by a desire to penny pinch even at the expense of your own safety.

Tibbot is correct, it is extremely important to ensure that the flue is correct. The seal will be different, its operating temperature etc...

it has to be the flue thats specific to the boiler