Worcester 8000 combi hot water flow rate

[rob7475]

Hi,

I had an WB 8000 life 30kw combi fitted in 2023. At the time our house was fed from a lead mains and the flow rate into the house was around 12lpm. Last year we had a new supply from a 4inch main and now have a 25mm supply pipe into the house. Pressure is good and flow from the cold taps is around 30lpm.

However, I've noticed that I still only get around 10lpm from the hot taps no matter what dhw I set on the boiler. I've tried temps from 35 up to 60 and still get 10lpm. Surely I should get a better flow if I set the boiler temp lower?

When the water supply enters the house, there is a cold garden tap in the garage before the supply goes to the boiler. This supply gives me 30lpm. The first hot outlet is another garden tap in the garage which is only giving 10lpm (No other hot taps in the house get more than this either). Are there any settings on the 8000 that limit flow rate for dhw?

There's also a valve as the cold feed enters the boiler - I'm not sure if I should try opening this via the screw at the bottom or not?

Thanks,
Rob

 

[rob7475]

just to add to this, I've tried turning the dhw off on the boiler so it doesn't heat it at all. This makes no difference and I still only get around 10lpm out of the hot outlets

 

[CountryFan]

There's likely a flow restrictor in the boiler so it doesn't give more than a certain flow rate so folk aren't moaning about poor hot water delivery from a combi.

 

[Johntheo5]

The DHW temperature settings have no bearing on the flowrate, just the temperature, based on the boiler output and flow.
Some boilers have restrictors installed to limit the flow to give a 35C dT (rise) in temperature so a 30kW combi should give a flowrate of 12.3LPM, if there is no restrictor and the DHW flowrate is, say, 15LPM then the dT is 28.7C so just cooler HW, if you switched the boiler off the flowrate will still be 12.3 or 15LPM.

Can you explain this or show a few more photos......
"There's also a valve as the cold feed enters the boiler - I'm not sure if I should try opening this via the screw at the bottom or not?"

 

[rob7475]

The DHW temperature settings have no bearing on the flowrate, just the temperature, based on the boiler output and flow.
Some boilers have restrictors installed to limit the flow to give a 35C dT (rise) in temperature so a 30kW combi should give a flowrate of 12.3LPM, if there is no restrictor and the DHW flowrate is, say, 15LPM then the dT is 28.7C so just cooler HW, if you switched the boiler off the flowrate will still be 12.3 or 15LPM.

Can you explain this or show a few more photos......
"There's also a valve as the cold feed enters the boiler - I'm not sure if I should try opening this via the screw at the bottom or not?"

The second picture shows the valve I mean with the slot on the bottom. I've checked it though and it's fully open. It does sound like there's a flow restrictor fitted which would explain what I'm seeing

 

[Johntheo5]

10LPM is a bit on the mean side but if you set the DHW temp to its max of 65C? then that gives 19.5LPM at 40C when mixed with cold mains water of a present 18C and in the debths of winter 12.3LPM when mixed with cold mains at 5C. Its probably only prudent though to set the DHH temp to say 55C to avoid scalding from a HW tap only so a boiler DHW flow of minimum 11.6LPM required to ensure the full boiler output of 30kW can be utilized from a mains temp of 18C. You can remove the restrictor and just control the flowrates at the users but I think different size restrictors are available so maybe aim for a DHW boiler flowrate of ~ 15LPM.

 

[rob7475]

Thanks for that. Are the restrictors easy to access or would I need a gas safe engineer to do it.

 

[Johntheo5]

Not familiar with domestic gas boilers so don't know but someone on here will probably advise.