Greenstar 28i junior HW performance issue

[shmelv]

As above the boiler is a 28i greenstar 5 years old and has always worked fine

Over the past month or so the Dhw has been struggling at full flow rate, for example if I run the hot water on full flow the water cools to a luke warm temperature but if the water is turned down slightly suddenly it is steaming hot and will stay hot,
Been advised to check the flow rate but it seems odd that it would be fine until recently.

The ch is fine and pressure is on 1.5 bar

Thanks

 

[joe-90]

Don't forget that the water going into the boiler is unusually cold at the moment - and that mean less hot water out.

 

[shmelv]

Don't forget that the water going into the boiler is unusually cold at the moment - and that mean less hot water out.

That was a thought I had, could it really make that much of a difference ? (I'm not questioning you just wondered if it can really make that big a difference)

 

[joe-90]

When heating water a boiler runs on full output - it can't put out anymore.

Therefore, if the water going in is 10 degrees colder the output is going to be a lot colder too.

 

[plumbplumb]

I'm not questioning you

I wouldn't bother

 

[Whitespirit66]

Firstly, please ignore Joe's unqualified advice.

If you have had the boiler 5 years, which equates to 5 winters, and the problem has only started recently - nothing to do with the colder incomming water. The colder water will make matters worse, but it is highlighting a problem with your boiler. A 28kw boiler should still provide properly heated hot water.

If the water in Bradford is hard, your boiler's plate heat exchanger may be scaled up. The primary side of the hex may also be partially blocked. Likely you will need the hex cleaned or a new one.

 

[Whitespirit66]

You aint gonna prove physics wrong mate - Nobel prize if you do.

Very good Joe. However, the OP want's proper advice, not someone seeking attention.

Don't upset the mods again.

 

[shmelv]

It's odd that if the tap is turned up full it loses loads of its heat, but turn it down slightly and it's steaming hot !

 

[Whitespirit66]

It's odd that if the tap is turned up full it loses loads of its heat, but turn it down slightly and it's steaming hot !

Not really. If your hw hex is scaled and/or blocked (usually with rust flakes from inside rads) it will be less efficient at transferring heat into the cold water.

As you slow the hot tap, the cold water flow through the hex slows. This gives the water more time to heat up, as it is spending longer inside the hex.

The colder water coming from the main will exacerbate the problem, but it's not the reason for it happening in the first place.

 

[skodaman007]

may be the last time it was serviced the flow rate/temp rise was not checked.
this boiler needs professional service/repair and installation just check your benchmark certificate and previous service/repair documents then phone the last gas safe contractor who serviced it.

good luck.

 

[shmelv]

So the likelihood is a blockage in the plate heat exchanger, because as you said it would have ,is behaved in previous winters aswell I'd have thought and this is its 5th winter !

Are these easy to remove and clean out or check to confirm the suspected problem

 

[bengasman]

You aint gonna prove physics wrong mate...

Do you mean the "laws of physics" by any chance? Probably not.
But proving your advice wrong, is very easy; happens several times a day usually..

Dear OP, before taking advice from Joe, you'd do well to check out a random selection of his posts. He is one of the resident trolls and most of his solutions are wrong, some are even downright dangerous, but luckily you can't see those because they get deleted.

Your boiler problem can be down to a number of causes and to determine which one is a bit hard to tell without doing some tests.

 

[shmelv]

Cheers ben ! Thanks for the advice, what sort of faults could cause this and what tests would need doing safely

 

[ukrobj]

He won't tell you mate because he doesn't know.

Common sense tells you that if the input is colder then the output will be colder.

Sadly, we all wished you had common sense, then your'd stop posting about things you have no idea about.

 

[joe-90]

Are you saying that it comes out the same temperature summer and winter?

If so - why do many boilers have a summer/winter setting?