Radiator plumbing question.

sarge123

basically i after some advice.:rolleyes:

In our new house we have a combi boiler (the same as our old house), but it is located under the stairs instead of upstairs in the airing cupboard in the bathroom (the previous owners had ripped out the airing cupboard to fit in a large corner bath, and hence moved the boiler downstairs).

The problem is my flow of hot water up stairs is terrible. It takes ages to fill up the bath. Downstairs the flow is better, not ideal but usable.

The outlet pipe on the bolier is 15mm, it then goes through seven 90 degree bends, then for some reason the pipe changes to 22mm, up the wall and then under the bath, it then goes back to 15mm to feed the bath, sink and then comes back down to feed the kitchen and downstairs toilet. I can only assume the flow of hot water downstairs is better due to the drop down ie gravity.

My question is this, is the rubbish flow upstairs due to the pipe changing from 15mm to 22mm as it goes upstairs (logically this would affect it as the water has to fill the larger pipe), but of course the pipe does change back to 15mm upstairs, so would the opposite happen ie pressure increase back to normal due to water flow from large pipe back to small pipe.

I can get to the 22mm pipe to change it to 15mm and also remove some of the 90 degree bends in the process. I just want to check that it would do anything before i do the job.

Also we have just had our annual British Gas take on initial service and all was okay with the boiler.

Many Thanks

Sarge

EliteHeat

What kind of flow rate and pressure do you get from the kitchen sink cold tap? and again for the bathroom cold taps?

What has this got to do with radiators?

sarge123

The cold tap flow / pressure is fine both up stairs and down; it is probably better downstairs, but it comes in where the kitchen sink and downstairs toilet is, then goes up to the bathroom, then down to the boiler. The water stop !!!! is turned on full minus half turn.

EliteHeat

So you are saying that the flow rate for hot water is better downstairs despite the fact that the route for the hw goes via the upstairs bathroom?

Have you measured the hot flow rates at the various outlets?

I assume you know already that combis are generally very slow for baths compared to hot water cylinders.

sarge123

It has nothing to do with radiators - my mistake. No coffee this morning....

Yes that it exactly what i am saying, the hot water flow although it comes via the upstairs first, is better downstairs at the kitchen; i assumed that was because of the drop...maybe wrongly.

I know that combi are slow, but really the upstairs hot tap to the bath is not really much above a trickle. Do you think that is because as the pipe changes from 15mm to 22mm the water loses all of it pressure?

EliteHeat

No, I think you have a duff tap on the bath.

You have been implying throughout the thread that you suspect frictional resistance from the tortuous hot water path and normally I would agree. However, the fact that you have satisfactory performance after the bottleneck rules this out. Gravity, will have little or no effect on the downstairs leg from the bathroom.

Next, peoples perceptions of low pressure and flow rate for baths after combi conversions are invariably skewed - the flow rate is just the same but the increase in bore size reduces the pressure.

But, a trickle cannot be mistaken for anything else, so in the absence of any other factors, the bath tap sounds like the culprit to me - maybe the washer is sticking to the valve seat.

sarge123

Many thanks for running that through with me. I will take a look at the tap.