replacing boiler

mm1985

We moved into our current house in January. We were very aware that the boiler would need replacing soon but, while we are able to get engineers out to quote us actually getting a physical quote is proving difficult. We have finally had a quote for £3200 for a 32kw worcester combi boiler. The price itself is not an issue but we are unsure if this is what we require for our home so are looking for a little advice.

We have a 4 bedroom detached house with 3 showers, the boiler engineer has told us that at present an unvented tank would not be suitable as the water pressure to the house is too low and to get these changed would cost a few thousand. We currently don't use more than one shower at a time and can't see this changing for a few years so he suggested we have boiler changed now and then in the future either look to have work done to pipes to house or change showers to electric. 

He also states that with the low water pressure that we would not benefit any further from a 35kw boiler.

Is there anybody on this forum that has the knowledge to confirm that this is all correct? We need the boiler changing within the next month and as this is the only person who has currently come back with a quote and has come recommended we are eager to get him booked in if all this is true.

Carrot007

Sounds about right?

Old house? Lead pipes to the main?

If so replace them. I have that in my last house. All it took was digging a 10 metre trench (big garden!) to the border and then the water company came and changed their bits and connected it (and left it off as it was over 10 metres and needed an extra few to get to the house! which I added later). Went from worst flow ever to fast as anything!

nofoollikeold

1. Sounds generally reasonable, but the pressure and flow requirements for a combi boiler are not all that different from those needed for an unvented hot water system.  
2. I'd suggest for a combi you would need:
2a. An absolute minimum standing pressure of 1.0 bar, more if you don't want to experience shower temperature changes if a tap is turned on / loo flushed at the same time. 
2b. A minimum flow rate of at least 12 litres per minute.
3. You might ask the installer who has quoted what the figures are, assuming he / she has tested them.  If they haven't been tested, I'd steer clear.

Jeepers_Creepers

As said above, what your plumber is saying is generally correct.

As NFLO also says, a combi that size also needs a good pressure and flow.

I disagree with NFLO on the figures, tho' (sorry pal), since 1bar pressure would be simply abysmal, and this would drop significantly as soon as a tap was opened. Ditto 12lpm flow - a 32kW combi should deliver a hot water flow rate of 13lpm and above, so having only 12lpm available, especially when a cold tap is opened at the same time, is just not enough. I hope, therefore, you have significantly more than this?

So that we can comment fully, MM, can you tell us what your cold incoming mains water flow rate and pressure is? Did your plumber tell you?

(You can check this yourself - stick a pan under the kitchen cold tap (assuming it isn't a restricted 'eco' type) and open it fully. Let it run for exactly 10 seconds, measure the number of litres in it, and 'times' that by 6 to get Litres Per Minute. Report back.

For pressure, this is far more complex and scientific - tell us how 'splashy' the cold flow is during the above test. Does it come out with obvious gusto? If you stick yer thumb firmly over the tap nozzle, can you stop the flow, or do you instead wet your pants?)

Is a combi ok for a large home? Yes, with the proviso said by all - it'll only serve one shower at a time.

What system do you have at the moment?

If the reason for your 'just ok' P&F is the supply pipe to your house - bearing in mind it could be an issue to do with a poor mains supply in the road, so you upgrading your pipe won't help much - then the best solution is to have this replaced. Have you spoken to your neighbs to ask what their supply is like, and what sorts of systems they use?

To fit an expensive combi now when you, yourself, say that it might only be for a few years, sounds a costly route to me. Fitting electric showers when you upgrade your incoming mains (assuming it'll help) is a compromise, because leccy showers are pants. They just are. Ok for a guest room or secondary en-suite, but for someone who has daily showers and enjoys them, they will disappoint.

I come back to - what do you have at the moment?

1) If it's 'vented' (a cold tank in the loft), then this in theory can continue to provide for all three of your showers, tho' they might need booster pumps.

2)If it's unvented, then you can compensate for a lack of mains P&F by installing a pumped accumulator - this can go in your garage, for example. That will give you everything you could possibly want...

3) If it's an old combi, what make and model? And how do you find it? (Don't say 'by walking into the kitchen...')