worcester combi boiler 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?

WIAWSNB

Confirm 100% that the blue lever is on the cold inlet - which is does appear to be; that's a shock-arrester, by the looks. Is the S-A a new addition due to your improved incoming mains supply? 

See the flat screw slot with a black plastic surround immediately behind that blue lever? That is the actual incoming mains shut-off valve, and it is correctly aligned with the flow direction = fully open.

I don't know what that blue lever is, and I wouldn't touch it until that's clear! It looks like a 'discharge' valve, where you'd press the lever in order to open a valve, but I don't know.

Do you have instructions with your boiler? If not, a copy should be available online. Or, 'Chat' with WB and ask them.

Which outlet has the best hot water flow in your house - a shower, for example? If so, take a flow reading there. 

Many/most modern household taps have eco flow restrictors built in. 

WIAWSNB

Just to add - 10lpm from a tap is pretty good, and should be perfectly fine for most purposes. 

If you like a good shower, then turning up the DHW temp should do this, as more cold would need blending in = greater overall flow. 

rob7475

Thanks for the reply. The blue lever is used to top up the pressure in the central heating. The shock arrester was fitted when the boiler was installed.

10lpm is fine when we only have one tap running but if I have the dhw set to 45 and open two taps, I still only get a trickle out of the second outlet. I'd expect a half decent flow out of two outlets if I have the water temp set lower. The boiler should have a dhw flow rate of 12.3lpm at a 35degree temperature rise

Albermarle

Could be an idea to phone WB, they are usually quite helpful. 

WIAWSNB

rob7475 said:

Thanks for the reply. The blue lever is used to top up the pressure in the central heating. The shock arrester was fitted when the boiler was installed.

10lpm is fine when we only have one tap running but if I have the dhw set to 45 and open two taps, I still only get a trickle out of the second outlet. I'd expect a half decent flow out of two outlets if I have the water temp set lower. The boiler should have a dhw flow rate of 12.3lpm at a 35degree temperature rise

"The blue lever is used to top up the pressure in the central heating." Ah, that makes sense.

The actual inlet valve, as I mentioned, is the screw slot behind this. No risk in you turning this to experiment, but it does appear to be fully open in that position - the slot in-line with the flow.

Most boilers have the option of a flow restrictor fitted on the inlet, usually fitted just after the inlet valve. It would have been a weird thing to have included with your initial installation, as your mains supply was just about adequate, but it still could have been. 

From what you've described when you open more than one hot tap, I have to agree it suggests a limited flow within the boiler itself, and not from the taps themselves. So I guess the obvious culprit would be an intentionally-fitted - or neglected-to-be-removed - flow restrictor. 

Have a 'chat' with WB - most of these companies are really good with customer service. 

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

FreeBear

The blue lever is part of the filling loop. You only need to touch it when topping up the CH system (same for the "screws" which are the ball valves).

According to the WB manual, there is an internal flow regulator - This can only be adjusted by a Gas Safe engineer. From the parts list, this flow regulator appears to be nothing more than a plastic disc with a hole in it. So "adjusting" flow rates means inserting a different disc with a bigger hole. No idea why the flow would have been limited to 10l/min as the 30kW model will give a 40°C rise at 14l/min...

There is also a strainer on the cold water feed - It is just possible that this is partially blocked, so limiting the flow rate. Again, being inside the boiler, you'll need a GS engineer to clean it - Get him/her to do it as part of the annual service.

WIAWSNB

Good points by FreeBear. I'd forgotten about the strainer - the one on my GW disintegrated, and the debris stopped the flow switch from spinning...

As you've sussed, Rob, turning off the boiler won't affect the actual amount of water flowing through the boiler - there is no electrically-governed flow valve inside. The 'flow' is controlled simply by the tap or other outlet being opened, and how far. The boiler should then fire up and modulate its burner in order to provide a steady water temp for that flow - open the tap further, and the burner should ditto. And vicky verka. 

Seems you need a GS to have a looksee. 

rob7475

I've got the annual service booked for next week so I'll ask the guy to take a look then.

I assumed that as I decreased the DHW temp at the boiler, I'd get an increased flow rate at the taps. If there's a flow restrictor fitted to the inlet though, that would explain things.

WIAWSNB

rob7475 said:

I've got the annual service booked for next week so I'll ask the guy to take a look then.

I assumed that as I decreased the DHW temp at the boiler, I'd get an increased flow rate at the taps. If there's a flow restrictor fitted to the inlet though, that would explain things.

That would be the case if the heater (the boiler) had a fixed power output, like electric instant showers do. 

Boilers 'modulate', so they turn the flame up and down to suit demand. The actual 'flow' is controlled by the outlet tap, but obviously limited to a max figure determined by the incoming mains - and any physical restriction.

Let us know how it turns out, please.