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Andrew Smith
Andrew Smith, Plumber
Category: Plumbing
Satisfied Customers: 3586
Experience:  City and Guilds qualified plumber
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Hi, we have a small 1980s 3-bed semi-detached house, and are

Customer Question

Hi, we have a small 1980s 3-bed semi-detached house, and are planning a loft conversion that would give us two additional bed-rooms. We currently have an open system, but want to convert to a sealed one. Also all pipes leading to radiators are micro-bore, but we expect they all have to be replaced, probably along with the radiators.

We're looking to get advice on what our options are, the specification of the new boiler, whether a combi with integrated hot-water-tank is suitable (we will have two shower rooms) etc.

How should we best go about getting good advice?

Many thanks,
Mike
Submitted: 2 years ago.
Category: Plumbing
Expert:  Andrew Smith replied 2 years ago.

Andrew Smith : It is all about hot water flow rate
Andrew Smith : Most boilers will cope with the central heating, but the hot water will determine the overall size of the boiler if you want to use a combination boiler
JACUSTOMER-xmkan2sb- :

Yes, I have read this before. But one of our remaining questions is whether a combi boiler is suitable in a scenario where two showers run simultaneously, i.e. one person has a shower, and then a second shower is turned on. I know this can cause issues (e.g. sudden temperature variations in the first shower). Does a combi boiler with integrated hot water tank address this sufficiently? Is there anything else we need to consider? Does an integrated hot water tank address other weaknesses of combis, e.g. constant hot water at a low flow rate?

JACUSTOMER-xmkan2sb- :

Space is at a premium, and that is one of the main attractions of a combi for us. But should we consider a system boiler & separate hot water tank instead given our requirements?

JACUSTOMER-xmkan2sb- :

If a combo with integrated water tank is suitable, what do we need to consider to decide on specifications (e.g. size of the integrated water tank)? What are good boiler models that should make our short list?

Andrew Smith : Your first question is water pressure and water flow
Andrew Smith : If both are poor then stored water and a conventional system with a gravity fed cylinder may be the best option and boosted water for showers
JACUSTOMER-xmkan2sb- :

Water pressure and flow are fine, and we are not considering an open system.

JACUSTOMER-xmkan2sb- :

I appreciate you sharing the general information re pressure requirements, but they don't address my questions.

JACUSTOMER-xmkan2sb- :

My question is how to get the right advice given our specific situation.

JACUSTOMER-xmkan2sb- :

When we first had a (worcester bosch) combi boiler installed in a previous place the pressure and flow were assessed as very good. But if, while having a shower, the got water tap was used in either the kitchen or the

JACUSTOMER-xmkan2sb- :

Sorry, if a HOT water tap was used... in kitchen or bathroom wash basin, there was a noticeable temperature change.

JACUSTOMER-xmkan2sb- :

After installing a high quality (Grohe) temperature regulation valve the problem was reduced, but not eliminated.

JACUSTOMER-xmkan2sb- :

We were told this was a 'feature' of a combi boiler. And that this problem could be addressed by using a combi with integrated hot water store.

JACUSTOMER-xmkan2sb- :

But I don't know whether this is true, and whether it is true in the case of the situation I have described (i.e. two simultaneous showers).

JACUSTOMER-xmkan2sb- :

If it is, I would appreciate some further info, e.g. recommended manufacturer & models etc.

JACUSTOMER-xmkan2sb- :

Alternatively I would be happy to know how to get this info.

Andrew Smith : A combi with a thermal store is a good idea but will still not eliminate the problem
Andrew Smith : You could use a pressurised cylinder if the water pressure and flow rate are good as this will be good for the showers, you could always pipe the outlets close to the thermal store directly from it if they are the high water flow items - bath, showers etc and run the additional outlets direct from the combi.
Andrew Smith : The reason I said a combi with a thermal store will not cure it as once the combi starts running water it is playing catch up and once it is expended it is only as good as the input of the boiler.
Andrew Smith : A worcester 42cdi would be ideal but would still be a worry if you want to run 2 showers at one, I can from mine and it is only a 37kW boiler but there is a definite drop in flow rate.
JACUSTOMER-xmkan2sb- :

Hi Andrew, can I just try to understand: the suggestion of the pressurised water cylinder would involve a system boiler, not a combi boiler, right?

JACUSTOMER-xmkan2sb- :

And the difference between that and the combi with thermal store is just that in the latter case the reservoir of hot water is smaller?

JACUSTOMER-xmkan2sb- :

So theoretically if we could find a combi boiler with a sufficiently large thermal store the quality of showers would be identical to the solution with the pressurised cylinder?

JACUSTOMER-xmkan2sb- :

If not, how would we notice a difference?

Andrew Smith : A pressurised cylinder can take heat from avenged system, a system boiler or a combi.
Andrew Smith : Depending which way you want to do it, you just have to change the zoniing
Andrew Smith : *zoning
Andrew Smith : A pressurised cylinder will hold 200, 300, or 400 litres and gets heated via the boiler at any time as would a gravity fed one, it just gives much more storage and the boiler is only playing catch up once about 1/3 of the cylinder is used
Andrew Smith : Most combination boilers with storage are only just bigger than a standard cylinder, so the amount of stored water is very much smaller
Andrew Smith : Sorry, just read it back - first answer should not be avenged, it should be vented!

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