New boiler

[RaspberryPi1]

Our current combi boiler is on its last legs. The divertor seems faulty and either have hot water or central heating! Had a plumber around, and the cost to fix is at least 350. Based on this we have decided to go for a new combi.

Our original plan was to do an extension in a few years and have a megaflo and system boiler installed. However this is now not possible!

We have a few central heating engineers coming tomorrow. Few open questions.

1. My research indicates that Worcester Bosch is the one to go for. As the current combi is in a kitchen cupboard, I'd like to go for compact. They do two ranges CDi and Si. Any preference between the two?
2. How much power to go for? We have a flow of 14 litres per a second, and 8 double radiators.
3. Powerflush - is this worth it?
4. Magnetic filter -again is this worth it?
5. Any recommended installers in South East London ? And what cost to expect?

Ideally we'd like to use this boiler when we upgrade to a megaflo (or equivalent), is this at all reasonable? Or is it likely we'd need to buy a brand new boiler at that time?

You'll get an additional 1 year added to your warranty if you add the magnetic system filter to your worcester boiler. I also got two extra years for using the 28CDi boiler over the 25Si, and for using the worcester controls bringing my warranty to 10 years total (having using an accredited worcester installer). So for this alone, it's worth it.

As for connecting an unvented cylinder like a megaflo to a combi, I think this is technically possible although I'm sure somebody else who knows what they're talking about will be able to answer correctly.

I don't know much about boilers, but I think most installers will insist on a powerflush these days??

Having removed and emptied a radiator myself, I can confirm that the insides of a central heating system that hasn't been flushed for a while are absolutely disgusting. Think black slime!!

I'm having an Ideal Logic boiler fitted soon, and will definitely be giving everything a good flush through!

you can fit a cylinder, vented or unvented, to any boiler. The boiler does not know or care if it is heating the upstairs radiators, the downstairs radiators, the cylinder, or any combination.

But warn the installer to include in his price and the actual work that it should include the possibility to easily add the extra pipes and motorised valves. It might benefit from pipe stubs being included and a bit more space above or beside the boiler.

Thanks for the replies. Very helpful.
Currently the flow is 14l per a minute. Is this enough for mega flo or should I be looking at a new line from the mains?

All the plumbers so far are suggesting the power flush and magnetic filters!

Have a 22mm copper pipe from your stopcock to the boiler and new cylinder and bathtap, it will cut out the avoidable constriction of internal pipes and fittings. Insist on full-bore valves and avoid narrow bore braided flexible hoses. They have ball-valves that are very small.

That way you will avoid making the flow any worse, and may make it a bit better. The hot bathtap and pipe are deliberately constricted with a combi, otherwise the water is cooler. You will not want that if you get a cylinder.

I am guessing it may be more convenient to do some of this work when you change the boiler, rather than ripping it out when you get a cylinder.

Very helpful comments. Quotes have started to come in. One plumber is offering a fernox filter instead of the Worcester Bosch one.
This reduces the manfactures warranty to 7years, but they are offering their own for 10y (not sure if this is worth anything !). Any thoughts on the different filters?

On the boiler front it's a toss up between 28/32 compact CDi or 30 Si. Tempted to go for the 28, but is there much difference between models?

the Fernox TF1 is a very good filter.

I don't know the WB one but it's probably a rebrand of one of the major makes. Some of the plastic-bodied ones have been known to leak. You'd better ask your installer why he prefers the Fernox.

(might be because the WB costs three times as much)

I get the impression that boiler engineers don't like to install new boilers without doing the powerflush. I was really annoyed by it and the extra cost it added, but looking back, it sort of makes sense - you're paying for a new boiler, wouldn't you want everything to be as close to clean and perfect as possible ? If things go wrong, they'd always be the suspicion that it wouldn't have happened if you'd had the powerflush.