New Central heating but problems, Please help

[Dale Sanders]

Hi.

hopefully someone can help me here.

I have a recently had a new gas central heating system consisting of 7 rads and a Worchester 36cdi compact located in the lofty controlled by the wave thermostat.

I used to have electric storage rads and the electric controlled heating with were on tanks.
after install i have a drop in hot water pressure. if the cold is on then the hot drops and even running the bath takes forever.

any ideas?
i want to make sure i have all my facts straight before speaking to the plumber who installed as he did come arounf measureing pressure and said it was about average on the set up up i requested.
the main in pressure was 3 bar and the flow was 14l/m with the hot being 10l/m.
thanks for your help in advance

 

[jtsplumbing]

You need to call back the installer to check water flow your about 3Ltr per min short on hot water delivery,

 

[Scott_1979]

Main stop tap fully opened? Isolaters under the boiler fully open?

 

[Dale Sanders]

He checked flow when I was present.
Everything is open.
I have 15mm that enter house that run in the loft but then goes to 22mm. Would it help to increase to 22mm from 15mm pipe.
The flow seems fairly quick on top taps on sinks but very poor on bath.

 

[sammathias]

All your outlets are 15mm to the hots but on your bath i presume its still old 22mm probably delievers the same litres per minute just seems slower.

 

[Dale Sanders]

Yes.
Is the set up correct? How i can I increase flow?
What seems to be the problem?

 

[sammathias]

The flow on your boiler will be preset. Im not 100% familiar with your boiler but id say 12litres per minute. Thus cant be adjusted.
As for the 22mm to the bath. Ideally it should be 15mm from a combi...you may find you have to draw off alot more water before it becomes hot.

 

[AWheating]

Tbh it's sounds like there's not much wrong. Your water main is giving 14lpm. Your getting a little less once the flow has been restricted by your pipe work and boiler. If you open the cold then it is sharing the 14lpm with your boiler, probably have less restriction than your boiler it gets more of the share.

 

[Dale Sanders]

So if I am getting 14lpm and it enters the boiler at 14lpm why isn't it coming out at 14 or even 13lpm.
Sure it shouldn't drop 4lpm.

 

[steadyon]

1. Your boiler will provide 13 lpm at a 40 degree temperature rise, plus or minus 15%. If you're unlucky, and its minus 15%, the maximum hot flow rate will be about 11 lpm. Also, the Compact ERP version has a flow restrictor to limit the flow necessary to ensure that 40 degree, which may also reduce the flow rate.

2. The hot (and cold) flow rate at the bath outlet will be lower than an open pipe immediately after the boiler, as it has to navigate the pipework and fittings / bends. Friction in the system will reduce the rate of flow.

3. With a tank system, the hot and cold flow rates are largely independent as both come from large stores of water, usually (in the case of a bath) via 22mm pipes. With a combi, the cold comes off the mains via 15mm pipe, and the hot also comes off the mains via the boiler, again with (usually) 15mm pipe.

4. It would help to know what the cold mains flow rate is at the point of entry to your property. This would give you the maximum possible flow rate for both hot and cold. Measuring separately at the bath taps doesn't give you a full picture.