Can't get hot water at a decent pressure

[driver8uk]

Hi,

I have an Ariston combi boiler. It's apparently about 5/6 years old, but we've just bought the house so I'm not certain.

The central heating is fine, and the water comes out nice and hot, except that I had to turn the pressure down on the inlet to the boiler to ensure that it is consistently hot. I have set the water temp on the boiler to 4 out of a possible 6. I've no idea if that's normal because the instructions I have do not actually give you any information, but it appears realistic at a glance! Now the pressure is OK, but not great - sufficient to run a slow bath. The problem is that it is not sufficient to run the thermostatic mixer shower in the bathroom. The only way that I can get hot water out of it is by turning it on so little that it's just a dribble. As soon as there is a decent flow it becomes luke warm.

So my question is, is this likely to be a problem with the boiler? It's been superficially checked by British Gas when they flushed my central heating out, so it's safe, but it does make a few clanking noises and stuff.

Am I being overly optomistic in expecting a decent pressure from the hot water supply, or would a fully-working boiler be able to produce this?

Thanks for reading this far!

 

[BoxBasher]

You have answered your own question.

I had to turn the pressure down on the inlet to the boiler to ensure that it is consistently hot.

A combi boiler has to reduce the flow as it goes through in order for the water to be heated. You can't get out more than you put in, and you have reduced the amount going in.

I'm sure one of the guys that work with heating will be able to provide you with a more detailed (and possibly more correct) answer to the question of whether you are being over optimistic.

 

[ChrisR]

It hinges on exactly how little is "so little".
If it's a 24kW boiler (what's the model?), you should be getting about 8 litres/minute at showering temp. Buckets are often 9 litres and marked.
If it's much below that you could have sludge/scale in your boiler, or another boiler problem.

 

[driver8uk]

It's either an A23 or A27, I'm not sure how to tell.

So if I run the tap at showering temp and I can fill up an 8 litre bucket in a minute then there's nothing wrong with it?

As for sludge / scale in the boiler, would this have been remedied when the system was powerflushed?

Thanks

 

[cross thread]

at 9litres a min you should expect a 35 deg rise in temprature so if cold is coming in at 20 deg it should if working ok get it to 55deg if the flow rate is right then the boiler is not working correctly could be scale or it may be pressure settings/sensors if b.g flushed it they should have tested the boiler settings as well