How do I work out what size a replacement boiler should be ?

[David937]

The actual boiler cycling happens when the flow temperature is set quite low as I discovered recently and it also happens when running just the attic zone, which has a 1.7kw radiator and 12kw of heat being in.

Or ch installers who do not know how to size the rad properly

Yes, I personally found our installers pretty old school, if only I had known more at the time.

They are probably installing so many systems with old size rads that run at 82/71 and telling customers not to turn the boiler down, so most of their customers will not benefit from full condensing efficiency.

 

[tonybhoy]

Anyway,chances of fitting a 42KW combi boiler(17 ltires hot water per/min) in a small flat with a heating load of only 9.8KW is not high is it?

It was only an example.

.

Yes and not a very good one. Much better to have used a smaller combi for your example ,IMO.

Ever work for goverment spin, ehr,publicity depts ?

No wonder the OP is confused and untrusting of heating engineers etc.

 

[Brian Lacey]

I have been following the responses with interest.
Perhaps my initial question should have been to ask what procedures/measurements/information would be required by a boiler installer to determine the size required.
My comment re' being sold the correct size boiler was just that, I wanted to know that what an installer recommended was correct and in order to do this I was seeking information. I did not realise that it was quite so detailed a job but that was why I asked. After all, it will be myself that pays the bill so seeking assurance did not seem to be the wrong thing to do.
This did seem to upset some people but I would have done the same for any outlay of money to a third party who would be recommending I buy something that he/she supplies.

Once again thanks for the postings.

 

[D_Hailsham]

You don't have to get a combi do you D_Hailsham?

No - and I have no intention of getting one! I was just pointing out the pitfalls associated with a combi, which seem to be sold as the solution to all heating/hot water requirements.

Many system and heat only boilers do not modulate as low as I would like (3kW) and those that do tend to be "unpopular" with the corgi guys on here; e.g. Ariston 3-12kW, Ferroli 3-18kW, WB 4-12kW, Vaillant 5-15kW, Potterton 9-12kW.

 

[David937]

We would have got a system boiler and an unvented cylinder but we just did not have enough space.

The Vaillant 400 series are not popular but what about the 600 series?

The 615 model modulates down to 4.9kw.

 

[gas4you]

The 600 series are very good, just as the 800 series.

I personally will not fit another 400 series. They are the only Vaillants I ever get problems with

 

[David937]

Thought so, my uncle has a 600 series ecoMAX boiler, been in for 5 years now but never had it serviced!. Neither has he got the 300 litre unvented cylinder serviced

 

[gas4you]

You better warn him about the silicone burner seal problem.

This affects all the Ecomax range of boilers as well, although Vaillant pretend it doesn't, just to save face and costs

He needs to get this serviced asap

 

[David937]

I'm not going to bother with that, he is stubborn old cow and insists on calling cow boys and when something breaks he comes to me and all I can ever say is get a proper RGI in.

Maybe I should tell him and say don't come asking me for help when your unvented cylinder blows up and your boiler melts.

 

[mogget]

I think you should warn him, even if he ignores you. That way, when/if it eventually fails, you will not feel responsible.

 

[David937]

Yeah I'll tell him and his wife and kids

 

[David937]

Just an update regarding the Ecomax 600 my Uncle owns, in case anyone does find it interesting

The boiler developed a leak when operating, he called me and asked what to do!

I told him to stop fannying about and instead of asking me for help all the time, get someone in to sort it out and give it a service etc, I also mentioned the seal fault yet again! I gave him the number of the guy that does our servicing whom we have found to be very good.....so what does he do?

He orders the new graphite gasket himself and gets his 'friend' to install it, his friend said to just let it leak until the whole boiler stops working

Boiler still not serviced and a bucket is under the boiler which is emptied whenever it leaks, it's not CH water leaking as the pressure never goes down, it must be condensate. I wonder how long this boiler will work for before giving up completely.