New Gas Combi Boiler Bad Hot Water Pressure - Need Help

[FrankyTheFrog]

Feb 2011 we had a Worcester Greenstar boiler installed & the central heating re-plumbed - old hot water tank & boiler were taken out. Since then the heating has been vastly improved but the hot water has been very poor to the bath.

Prior to the new boiler the kitchen sink used to have very poor hot water pressure but now that is good, the bathroom sink is ok & the bath is utterly rubbish - it literally takes 30 mins to fill a bath to a decent level!

We had refitted the kitchen changing pipes & taps prior to the new boiler installation which had no effect on the old system.

We've just had a bathroom refit, new pipes & new taps but still have the same problem on the new system *very disappointing*

All water pipes in the property are now new & so are all the taps.

We live in a bungalow up quite a steep drive if that's of any relevance.

Help/advice would be very much appreciated please

 

[Dan Robinson]

Which greenstar is it?

How big is the bath?

 

[FrankyTheFrog]

Forgot to mention we had the internal stop cock replaced last week thinking it might help as the old one was stuck - no effect.

Piping is 15ml from boiler through to taps. Bath pipe then goes to 22ml for approx 20cms & into the taps (always has been like this even on the old heating system when we got good pressure). Mix of new good quality copper & new plastic

The boiler is either the 24i Junior or the 28i Junior judging by the manual - I can't get to it to check the exact model as we still have a load of boxes from the brand new bathroom suite blocking the way.

The boiler goes up to 5bar. We can fill it up to 2 (which is within the green) but it always drops back down to 1 where it stays unless we bleed the radiators in which case we refill it. Around 0.5bar is in the red & above approx 2.5bar

The bath is 1700mm x 650mm, depth at deep end 33.5cm (same size as the old one) - its classed as an "eco bath" & we don't fill it to bursting.

 

[Dan Robinson]

Can you measure the flow rate?

Are there any kinked hoses under the bath?

24 or 28? it is an important distinction.

What do the installers have to say about it?

 

[FrankyTheFrog]

Got to the boiler - its a Greenstar 24i Junior Combi Mark III

We're very new to this - how would we go about measuring the flow rate?

No kinks in any hoses.

Our plumber says its likely to be the boiler or pipes coming into the property from the main water line. Every pipe internally has been checked & where needed replaced. We haven't paid for boiler work & don't want to if unnecessary.

 

[Gasguru]

The old system had a large water cistern to feed the bath taps. Flow rate was only limited by the pipework/taps to the bath.

The bath taps are now fed directly from the mains...the flowrate is limited by the mains water pressure and boiler heat output. Combi boilers (especially the lower output types) will always mean slow bath filling. A 24 or 28Kw Combi will only provide 10 to 12 litres per minute of water at bath temperature. That's the downside of a combi.

The boiler goes up to 5bar. We can fill it up to 2 (which is within the green) but it always drops back down to 1 where it stays unless we bleed the radiators in which case we refill it.

The gauge shows the system pressure, it has NOTHING to do will the bath water flowrate. The gauge on the Worcesters normally goes from 0 to 4 bar. For a typical property you should set the pressure (when the radiators are COLD and the boiler is not running) to 1 bar. This allows a sufficient margin for the pressure to rise once the heating is on. On no account should it be more than 1.5 bar cold pressure. Otherwise the pressure can rise too much once the heating is on. If the pressure were to approach 3 bar the safety valve will open. Safety valves rarely re-seal once the pressure reduces. On the Worcesters replacing the valve is major agro....checking the pressure is very important on this model.

I suggest you check the safety valve pipework is not dripping....look at the 15mm pipe going outside.

 

[Agile]

Lets assume you have a standard 24 kW boiler. That will give about 9 litres per minute during the summer, less in the winter!

That will fill a typical bath to a utility level ( not film star ) in about 14 minutes!

What does yours really do?

Tony Glazier

 

[FrankyTheFrog]

The gauge shows the system pressure, it has NOTHING to do will the bath water flowrate. The gauge on the Worcesters normally goes from 0 to 4 bar. For a typical property you should set the pressure (when the radiators are COLD and the boiler is not running) to 1 bar. This allows a sufficient margin for the pressure to rise once the heating is on. On no account should it be more than 1.5 bar cold pressure. Otherwise the pressure can rise too much once the heating is on. If the pressure were to approach 3 bar the safety valve will open. Safety valves rarely re-seal once the pressure reduces. On the Worcesters replacing the valve is major agro....checking the pressure is very important on this model.

I suggest you check the safety valve pipework is not dripping....look at the 15mm pipe going outside.

I haven't often filled it to 2 as I quickly learned it shouldn't be higher than 1-1.5 but just put it in as an example. It was when I was first learning how to bleed radiators & yes I did the classic newbie thing of bleeding til the water stopped spitting thinking it was releasing all the trapped air. Consequently the boiler pressure dropped off the scale & it didn't work - a quick call to the installers sorted this & its been fine on that front since. It is usually on 1bar when the heating is off & still on 1 when the heating is on.

There is a constant wet puddle outside but I don't know if its coming from the copper pipe which I assume is the safety valve pipework or just condensation off the vent which billows steam when the boiler is working whether its 25 degrees outside or -10.

 

[FrankyTheFrog]

That will fill a typical bath to a utility level ( not film star ) in about 14 minutes!

What does yours really do?

To get the water literally about 5-6 inches deep for the baby to sit in would take about 14 minutes including adding a bit of cold to make it cooler - to get it a little warmer for an adult to sit in it with the water covering your legs but still not deep a lot longer. Its honestly atrocious - my parent's have poor hot water pressure in their bathroom from a water tank but nowhere near as bad as ours running off the combi.

 

[Dan Robinson]

You need to measure the flow rate at different taps and compare to the bath fill.

use a measured container and time the number of litres per minute are produced.

You should expect 9.

If the other outlets are OK then you know there is a problem with the bath supplies/taps.

If they are all affected then it would be worth checking for a blockage in the inlet valve of the boiler.

You said the boiler was fitted in February - then it is still under warranty. Call the installer?

 

[FrankyTheFrog]

You need to measure the flow rate at different taps and compare to the bath fill.

use a measured container and time the number of litres per minute are produced.

You should expect 9.

Are we talking measure the hot then the cold flow rates or just the hot?

 

[Dan Robinson]

Just the hot.

 

[FrankyTheFrog]

Just the hot.

Will give it a go when the boiler is back on later today - thanks

 

[Agile]

You need to get a bucket or saucepan of known volume ( can check by filling using a measuring jug. ).

Then time how many seconds it takes to fill this container. Measure at kitchen cold tap and then at bath cold tap and then at bath hot tap.

It seems as if a combi has been specified without the essential prerequisite of measuring the dynamic flow rate.

The mains flow rate is usually mainly determined by the pipe between the street and the house. Replacing this with larger bore plastic pipe will usually solve the problem but costs £600-£1200 typically.

Tony Glazier

 

[FrankyTheFrog]

You need to get a bucket or saucepan of known volume ( can check by filling using a measuring jug. ).

Then time how many seconds it takes to fill this container. Measure at kitchen cold tap and then at bath cold tap and then at bath hot tap.

Thanks for that Tony - have done so & here's the results:

1ltr jug
Cold Kitchen Tap: 6.5s
Hot Kitchen Tap: 9.5s
Cold Bath Tap: 5.5s
Hot Bath Tap: 9.5s
(also did cold & hot bathroom sink taps which were exactly the same as the bath)

We have concluded that our hot water pressure in the kitchen only appears so vastly improved cos it literally used to trickle taking an eternity to fill the sink for washing up!

Anyway, these figures work out that we're getting approx. 9ltrs/min of cold water from the mains & 6ltrs/min of hot water from the boiler - nowhere near the 9ltrs specified by another member on this thread.

Am I right in deducing that its more than likely the pipe coming off the mains, up our drive & into the property? Or is there a setting on the boiler to increase the hot water pressure?

I'd like to add that its been in the 20's heat wise for a couple of weeks now so surely there's no reason why the boiler should've "slowed down" to that?