Hot water is only warm

[Ashley Rosindale]

Firstly, apologies if this is in the wrong area of the forums.

I've just had a new Viessmann Vitodens 100 30kw boiler fitted on LPG, the CH is not fitted yet with only one small radiator as the load.

Problem is, DHW is at the upper end of warm, after 5 minutes of running the water, I can comfortably hold my hand under the water.

I've checked CH loop pressure and it is just over 1bar, flow rate is good and hot water temp setting on the boiler is max at 60 degrees.

Any ideas?

 

[footprints]

Might be the water flow rate is too high, I'm assuming this is a combi, there will be a litres per min flow rate quoted, it can only heat a certain amount of flow at a time, and it will not guarantee a final temperature only the number of degrees it will raise that flow by (if the water coming in is almost freezing the final temp will be less than if the water is at say 15deg.) try reducing the flow through the tap.

 

[Madrab]

Do you know what the outlet temperature actually is?

You'll need a weir gauge and thermometer, check what the mains cold water temp and the flow rate and then see what the flow rate and temp rise is through the boiler, 35Deg rise is the usual target at a specified L/Min.

 

[JohnD]

You'll need a weir gauge

or a bucket and a watch with a second hand (which the OP more likely has)

 

[Ashley Rosindale]

Flow rate is high, exactly what flow rate I don't know yet. Yes, combi boiler.

Agricultural I know, but I used a small thermos and ran the water into it for a few minutes and the thermometer reader 40 degrees.

Maybe I need to get the RGI back?

 

[Madrab]

or a bucket and a watch with a second hand (which the OP more likely has)

Or if it's a newly fitted boiler then the professional who fitted/commissioned it should have one and should have confirmed the output as part of the benchmark

 

[copea]

Agricultural I know, but I used a small thermos and ran the water into it for a few minutes and the thermometer reader 40 degrees.

In which case the boiler is likely to be functioning correctly.
As stated above, the flow rate is normally quoted at a 35°c rise.
At these times of year, the incoming water from the mains is potentially close to 5°c, giving you your 40°c.
The only way to raise this is to slow down the flow rate through the boiler.

 

[Ashley Rosindale]

I have just reduced the flow rate by approx 1/3, & the water temperature has increased to an almost acceptable level.

But my old boiler (a cheapo one) was able to produce scalding hot water during the winter months without a reduced flow rate, albeit mains gas and not LPG (if that makes a difference?)

This can't be right? If the boiler and system was older then maybe..

What are my options if indeed the boiler is functioning correctly yet my expectations haven't been met?

 

[Ashley Rosindale]

Installer recommended this boiler as he allegedly one fitted at his home (as you mentioned)

 

[Doggit]

Somethings not right, so get him back in. The boilers okay, so you won't be disappointed once it's working properly.

 

[Ashley Rosindale]

Will do, I'll keep u all posted. And thanks for the advice.

 

[muggles]

I have just reduced the flow rate by approx 1/3, & the water temperature has increased to an almost acceptable level.

But my old boiler (a cheapo one) was able to produce scalding hot water during the winter months without a reduced flow rate, albeit mains gas and not LPG (if that makes a difference?)

Age and gas type aren't relevant. What is relevant is boiler power output - if for example your old boiler was 35kW and the new one is 24kw that would account for the difference in performance. Do you have this information?

 

[Ashley Rosindale]

I was only referring to the plate heat exchanger and some possible build up of calcium etc in my older boiler (I had it changed twice in its 10 year life span)

The old boiler in my old house was a (don't laugh) Ravenheat 30kw Despite being a cheap unit I was happy with its performance, especially with my dirty water supply.

 

[Ashley Rosindale]

The new subject boiler is a viessmann vitodens 100w with a power output of 30kw.

 

[muggles]

OK so performance should be approximately the same for both. Does the general water pressure seem higher in your new property than your old one?