Combi Flow Rate

[mo7]

Hi

I have the following boiler

Ariston Clas He 30

Gas Boilers, Combi, CLAS HE Combi

This has a DHW of 12.9 which I presume is something to do with the flow rate.

This system was installed around 2 years ago. Whenever we have run the hot tap in the bathroom you give it a second to warm up and then it goes hot. The quicker the water comes out the less hot the water becomes.

I basically understood it to be - the combi is heating the water as it comes through, the quicker you release the water the less time it has to heat the water, hence it comes out less cold.

For this reason we use an eletric shower.

Now I have had someone round to look at my bathroom and we got talking on showers and he suggested a mixer shower but I said my boiler cannot provide hot water quick enough.

He said that it should be able to maintain to reasonabley constant temp (esp if it can hit a flow rate of 10 (which is why I have looked up the flow rate above)

I have read bits and bobs online about flowrates but generally speaking should I be expecting moreo ut of the boiler or am I getting average performance?

When we run ti slow the water is hot enough, but we have to run a bath slow to get it hot enough.

This article explains things well

[DLMURL="http://www.tcosgrove.co.uk/2008/11/understanding-combi-boiler-hot-water-flow-rates.html"]Understanding Combi Boiler Hot Water Flow Rates (T. Cosgrove - Plumbing and Heating Services)[/DLMURL]

thing is we have really good cold water pressure and it looks as though the pipes feeding the boiler are 22m, so whats wrong? He says 28kw is sufficient for a boiler...

Should I be asking the manufacturer for their opinion or calling in an expert?

 

[gasmarc]

you have an issue with dirt in the plate to plate heat exchanger or maybe under gassed ,has it ever worked correctly

 

[tipintim]

I advise all customers to have an electric shower fitted where combis are concerned.
So when your boiler breaks down at least you can wash.

 

[gasmarc]

or better still have a reliable boiler ,electric showers are expensive to run

 

[mo7]

if by correctly you mean has it ever consistently provided hot water at all rates coming out of the tap - no.

the 2 things you suggested, are they easy fixes for a heating expert?

 

[gasmarc]

yes no problem ,it could be dirt in your heat exchanger it could be under gassed or you may have a dodgy thermistor , there is someone on here who is repairing 3 aristons tomorrow so he might be able to enlighten you some more ,good luck

 

[Billy Bob Bob]

or better still have a reliable boiler ,electric showers are expensive to run

nah like the ad used to say,aristons go on and on,thats why i have 2 micro genus he and a a23 to fix tomorrow showers always work better off a combi or unvented compared to asthmatic electric,good point though it is having one as a back up i only have a 24kw combi( i am tight)and it gives a good shower no effort so a 30kw should work rather well in the op,s case and as already said somethings wrong ,so you need a gsr to sort it out or ariston if its in warranty,and all the things gasmarc has mentioned could be at fault

 

[pauls]

i came accross a problem like this a few months ago on an old combi (it was ready for the knackers yard ) i adjusted the flow switch and it sorted the problem

 

[gasmarc]

Cheers Gas Man I remember that I installed a load of the micro genius 2 as they were cheap ,unfortunately loads of them are still going strong and that is easily 10 years or more,

 

[Billy Bob Bob]

so did i 150 altogether mk1 and 2 not bad he though is a nightmare,and diverters and pcb,s failing en mass,plate heats also starting to play up and dont start me off about diverter bushes

 

[mo7]

I will give Ariston a call tomorrow

If its out of warranty presumably they will charge a lot to fix it?

Better of getting a central heating type?

Anyone know anyone in southampton that could come and have a look.

 

[gasmarc]

I hate the pcbs on them to much agg fortunately i only repair the simple things on them lol, the diverter on those leak down onto the thermistor which causes major havoc

 

[Billy Bob Bob]

or the pcb which blows up

 

[gasmarc]

i will keep them ones for you lol , i had one of these newer he ones that was playing up with all the spare tiny pcb boards , i told the customer to get ariston out engineer changed pcb and said there was sod all wrong with the old board and the problem lay elsewhere damed if i can remember what he said but i still have the board in my van , must be well expensive now

 

[aggis]

It's alright having a correct flow rate, but if the water pressure's too high you won't get the correct performance. Most manufactures test boilers at approx 2-2.5 bar.
If all is set up correctly a shower mixer t/static with a combi will out perform an electric shower.
True the advantage of an electric shower is that you'll have hot water, when & if your boilers broke.

 

[Bernie2]

Agree with aggis!

Mains water flow and pressure have got to be right for the installation before you will get the performance from the boiler.

 

[Blackcatgas]

your boiler should provide 12.9 ish litres a minute @ 35 degree rise, take a thermometer take the temp of the cold tap, it could be for example 8 degrees, then take a 15 litre bucket, set the hot tap running so that it fills 12.9 litres of the bucket in a minute, once the tap is et up to provide 12.9litres a minute (or there abouts) take the temp of the hot water coming out. it should have heated the water 35 degrees above what it was when it was cold ie 8 degrees+35 degrees the water temp should be 43 degrees, if this is right then there is nothing wrong with your boiler.
alot of people are disapointed with thier combi boiler because the water is not scalding hot like it used to be on the old system.

 

[stevetheplumber]

a 30kw boiler should give you great shower check flow rate and temp as described above if its not making what it should have the boiler checked for low gas preasure

 

[mo7]

Hi
I will get a pro in to take a look at it.

If I can get nice hot water coming out I might buy one of those showers where the shower head comes on the bath tap - presumably that saves having to plumb a new set of pipes in for the shower alone.