We have an ageing lpg boiler which heats 4 bed bungalow and big hot water tank, 2 power showers are often used simultaneously or in rapid succession.
We have shied away from combi boilers as there has never been a convincing answer to how the showers would be with a combi.
Bloke from British Gas was in yesteday to do the annual service reckons it is possible to retain cylinder and have a combi boiler installed, not heard of this before and he was talking a lot of nonsense about other things so I thought I'd ask on here as I'm sure the opinions will be more honest and independent!!

So is it possible and what are the pit falls/ problems anticipated, obviously some of the energy savings asociated with combi boiler are disappearing if tank is kept?Thanks
Mike

Yes I believe you can have a hot water storage tank with a combi.

If the BG gas guy was a heating engineer then he should know...

you can have a combi boiler with a built in tank of water like a worcester highflow where you could get up to 25 litre a min hot water
worcester
or you can have a normal boiler with a unvented cylinder you cant connect a combi to your existing cylinder

nearly all combi boilers now store a small amount of hot water (about 3-5 litres), some have an option to store more. theres a vailant combi, the 937 i think, that stores over 30 litres!

ive just changed from a 150l tank and conventional boiler to a 30kw worcester combi - NEVER going back to tanks and stuff. this thing is superb!

Thanks, some interesting links to explore seems like things have moved on quite a lot recently.

atb
Mike

I have a combi that also heats a hot water tank by pumping heating system water through a large coil in the tank.
I am not convinced about how hot the water is heated in the tank. I do also have an electric heating element in the hot tank.
The system in the house is... electric shower in the family bathroom, ensuite shower straight off the combi as is all the hot in the house except the ensuite which has all the non shower hot water from the tank, sink, bidet, bath

I have a Worcester Greenstart 37i which has no problems providing a good shower. The main thing is having thermostatic valves to isolate any pressure imbalance when other things are turned on.

Actually thermostatic valves on their own are not so good. The wax elements inside take a few seconds to work and when someone suddenly nicks a load of cold water (e.g. flushes the loo) you can get a sudden hot shower with potential risks attached. Okay, the scalding hot shower will only be for two or three seconds but it's still a risk.

A much better option is to install a pressure equalising valve on the supply to the shower. I've got one on my combi supplied shower and it's great. If the loo is flushed the amount of water coming out of the shower reduces but the temperature stays the same. They're about £40 from BES. And you can even use them in combination with a thermostatic shower. The PEV is also very easy to retro-fit (as I did).... I'm definately going to install them in my new place.

I have a Baxi with small internal tank - system is good but Baxi is unreliable though it happily supplies 2 showers at once. Both showers have internal pressure equalising valves, and, as mentioned, they work extremely well when other demands are made on the system.

The biggest limitation with a combie boiler will be the amount of water actually coming into the house through the main. With power showers (pumped) you could be using 20litre/min per shower but drawing this from a tank for short periods isn't a problemb. if you have a 1/2" / 15mm main into the house youve probably only got 20-25 litres/min coming in.

There is no reason why a combie boiler couldn't heat a hot water cylinder with a separate zone installed on the central heating side but why would you want to have two hot water circuits (the hot water from the combie and the gravity feed hot water in the cylinder cant mix)

Starting from scratch i would install an unvented cylinder with the water supply pipe sized for the demand but if you already have pumped power showers fit a new high recovery cylinder and a fully modulating condensing boiler and keep the layout youve already got.

Kev

quote:

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Originally posted by BenB
Actually thermostatic valves on their own are not so good. The wax elements inside take a few seconds to work ...

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Thanks for above. I have the gas board's engineer coming to do some sort of energy audit to find thre best / most efficient boiler set up for us, on Saturday morning - no obligation, at least I have a few questions to ask now.

atb
Mike

UPDATE
Gas board guy called and yes the only solution is the Worcester boiler which they buy for aroungd £1100 by the time he had banged ina few bits and pieces he came witha price of £4.3 I quizzed him about the £2.7k cost of moving existing pipes from floor standing to wall mounted position and bricking up half a dozen bricks for the old flue, he then proceeded to chop off varoius discounts bringing it to £3.7- £3.5 ish which I am guessing is somewhere near what a local gas fitter would be asking.

anyway thanks for the above pointers which helped our discussions nicely
atb
Mike

I dont like telling people what other plumbers should charge but British Gas are total rip of merchants. I pay less than £1100 for a Worcester 30CDi including flue and vat so British Gas will be paying considerably less.

Get some quotes from local gas fitters.
Make sure there gas safe registered and ask to see there id.
Check them out in terms of there appearance (tidy dress and able to string together a sentence) and take a look at ther van. Is it clean, if you can get to look inside is it tidy (not just tools chucked in etc)

You should get a quality gob for less than that and some Worcester accredited engineers can give you a 5 year warranty on the boiler provided you have it serviced regularly.

Kev