Vokera Linea 24 DHW issue

[Maboza-Ritchy]

Hi
Had the above combi almost 12 years and generally works fine. The issue is with DHW during the winter months. Outhwith winter DHW & CH is fine. During winter (right now) the DHW seems only tepid wether it is out of the tap or mixer shower. The CH on the other hand is fine ie radiators hot when they should be on. The only other thing I've noticed is the DHW tends to be a wee bit warmer during in the evenings but still not as warm as it should be.

Is there likely to be something wrong with the boiler or is a 24Kw not up to the job?

Appreciate any help with this.

Steveo

 

[nickso]

measure the flow rate from the taps. the 24 will only give you a 35 degree rise at around 10 litres a minute.

 

[Agile]

Almostly certainly your problem is as a result of the fact that the mains water is only coming in at 2-3 degrees during the winter and you boiler only has 24 kW available to heat it so it does not get as hot.

The solution is to reduce the flow rate at the tap to about 7 litres per minute which is about all it can heat up to the 43 degrees which starts to feel warm.

Tony

 

[DP]

Almostly certainly your problem is as a result of the fact that the mains water is only coming in at 2-3 degrees during the winter and you boiler only has 24 kW available to heat it so it does not get as hot.

Tony would agree partially with your statement only.

Regardless of the boiler size, terminal delivery at stipulated flowrate will be down irrespective of heat output. What I am saying is, hotwater delivery is quoted for 35 degree C temperature rise for flowrate specified. It does not matter how BIG the boiler is, if the tap is run fully open to deliver what the boiler is SUPPOSED to, hot water will only reach lowly 37 to 38 degrees C if cold water is 2 to 3 degrees centigrade.

 

[Maboza-Ritchy]

Hi all
Thanks for the replies.
I've turned the valve where the cold water comes into boiler to 45 degree position to reduce the volume of cold water entering boiler and it will be only after the next shower I'll know if this makes a difference. The funny thing is that whether using the shower or HW tap and turning the tap to nearly off (shower trickling) it still does not get any warmer. I would have thought that by reducing the flow rate at the output would have the same effect as reducing the flow with the cold water entering the boiler. Is that correct?

Anyway I'll see what the shower is like tomorrow and let you know.

Thanks again for your input.

 

[snb]

As this boiler is 12 years old it is likely that the is build up scale witin the dhw plate exchanger.

This will reduce the heat transfer performance greatly and will certainly be noticed when the incoming temp is down to around 4 or 5 degrees.

Any competent gas engineer will be able to check the flow/return temps on the plate exchanger to determine if this is the case.

I have descaled loads of these but you never get them as good as a new one due to be unable to get to the center of the plate.

Theses plate exchnger are not a lot of money. look on abcotuk.co.uk

 

[DP]

I am quite sure there is no limescale in Ayrshire.

OP, when you run the hot tap, what does the digi display indicate (this tells you how hot the HW is when hot tap is run. During CH demand, display indicated water temperature to radiators.

Boiler should have a flow regulator that limits the flow of water to hot taps which is often removed to then flood the hot water heat exchnager thereby requiring manipulation of hot tap to get hot water.

 

[Maboza-Ritchy]

Hi all
Had a shower this morning and even with cold inlet turned back a bit there was virtually no difference in water temp. The CH seems to work fine with all rads warm/hot when required. Could it be the heat exchanger that needs replaced? could it be the divert valve? or is the boiler at 24kw inadequate?

 

[Maboza-Ritchy]

Hi
Update on the saga of DHW issue.
With CH off at the clock, rads cold as you would expect, turn on DHW. DHW only luke warm display showing 28c. Rads start to heat up, left DHW running for a while the 22mm flow pipe for rads gets very warm while DHW remains luke warm. Turn off DHW boiler temp goes to 62c.
I have notice that later on in the day (evening) the DHW does get but it varies in temp from day-to-day.

Does this point to the divert valve being sticky? If so, can someone tell me what to look for to check if this working or not? I see you can purchase service kits p/n T0063. Is this easy enough to fit?

Would the motor divert vavle p/n 2905 need replaced too?

PS Present skill level. I'm a good all round DIYer and an electrician to trade ie 4 year apprenticship 1970, not a 6 week wonder.

Thanks in advance.

 

[nickso]

if there is heat going down the CH pipes on DHW demand then the diverter needs new seals and cleaning out.

get the diverter service kit and replace the bobbin, it's two seals and the 8 shaped seal. clean the brass seats that the bobbin seals sit on, they will be black and need to be cleaned back to brass. clean the diverter pin too, it may have stuff stuck on it.