Combi Boiler and Microbore piping - compatibility

[Curious Cat]

I'm about to have a combi boiler installed - as we are having a loft conversion (hence need to get rid of the tank in the loft) and could also do with better power to our shower.

We live in a Victorian house and have microbore pipework.

We've been told that we need to have the microbore pipework upgraded as it won't cope with the power of our combi (30 KW), and also that a power flush is necessary.
Total cost quoted: �2740

1) Does this advice sound right or superfluous to requirements?
2) Re. combi boiler - we're probably going to go for a Vaillant or Worcester-Bosch. Any strong reasons why not to use either?

Thanks!

[terence7556]

a power flush is essential
as for the boiler make they are near the top of the tree but read sep 07 which at the library for boiler comparisons report for comments from users

[gasman]

Yes I would very strongly advise upgrading the microbore, A power flush should always be performed it is essential infact if not performed could invalidate any warranties Worcester/Bosch or Vailliant are both superb boilers and I install / recomend them myself to customers. As for the price you quote it is quite fair and not a total rip off.

[sense4all]

For similar reasons ( loft etc ) we had a new combi boiler Vaillant . It was not really good enough for a busy five bedroomed house ... now we have a new sealed system also Vaillant which is loads better and this time we replaced our megaflow water unit at the same time. A thousand times better.

[gucciman]

microbore pipe is never a good idea as over time it is going to silt up and become restricted which will affect the efficency of your heating system.
power flushing is a good idea, british gas charge around 650 for this but smaller independant firms do it for around 400.
i am currently training as a heating engineer but my father/boss whos been in the trade for 48 yrs rates the worcester bosch greenstar as the best boiler on the market, he also highly rates vaillants.

[MrMicrobore]

The answer to your question has nothing to do with your new boiler being too powerful, but depends on whether your microbore system provided adequate heating in the rooms previously. If the microbore system was adequate before, it will be adeqate still when connected to the new boiler assuming the original boiler had sufficient heating output to serve the radiators. A good heating engineer should be able asses this correctly rather than the rather stupid recommendation you have been given. If you are extending the heating system to the loft rooms, It will be an easy matter to run an additional circuit to this area direct from the boiler to avoid overloading existing pipework.
,
It is also an old plumbers tale that microbore system silt up. This can only happen if internal corrosion is occurring or fresh water carrying calcium and other deposits is entering the system to replenish leaks and other system faults. If the system was properly installed and has been well maintained the system water will be reasonably clean if not rather black in colour. Check the requirements of the new boiler manufacturer's. They may require a power flush or just specify a good flush with a special central heating cleaner.

My first impressions of your proposed installer are not good and recommend you get a second qualified opinion.

[Surreyplumber]

Power flushing microbore has limited results due to low flow. Try having it powder flushed, the abrasive powder is much more effective at cleaning the small pipes. The PowerFlush Association has members that do powder flushing.

[Surreyplumber]

Microbore is a nightmare to power flush: The association now has nationwide specialist members that deal with microbore on a daily basis. The average power flush company will not get the same results.

[MrMicrobore]

If your Microre system is working satisfactorily on your present system, it will give the me results with a combi boiler. The main reason why your combi boiler is rated at 30 kW is to provide sufficient instantaneous hot water generation. Your house heating requirements will remain the same. Many boiler manuafacturer's require an old system to be power flushed in conjunction with the installation of their new boiler. A properly installed microbore system or any other system for that matter will not silt up. If it does there is a problem, such as a leak or air being drawn into the system etc. I installed my first microbore system in 1958 and have never had a problem. The two boilers you mention, both have a good reputation.

Mr. Microbore (system originator)

[idkwia]

Mr Microbore - very interested to read your comments here. I have a microbore system that works well except that one of the radiators downstairs doesn't get warm or hot at all and this is not due to there being an airlock. British Gas engineer came and said it was probably full of sludge and suggested a powerflush but said that British Gas will not powerflush microbore sytems. He suggested that I should search to see if I can find a company that does powerflush microbore systems. In view of your answers on this thread I would welcome your suggestions please.