Worcester Bosch R35 HE Plus Combi - Flow Rate

[NigelCollins]

I have the above boiler and am getting a flow rate (measured from 2 different taps) of just over 7 litres / minute. The quoted flow rate (with a 35 degree rise) is 14.6 litres / minute. I realise with outside temperatures (and therefore water input temp) low that I wont get 14.6 l/m but should I expect the rate to drop that much? Thanks

 

[Dan Robinson]

Are you saying you have to lower the flow rate to 7 litres per minute to get 35 degree rise?

 

[NigelCollins]

Hello Dan, no I'm saying that as the boiler is set at the moment I'm only getting 7 l/m. The HW stat on the boiler is set just below the 'dot' so as I understand the range to be between 40 and 60 degrees its probably set to 55 degrees. I'm guessing the incoming water temperature to be 5 degrees so that means the boiler has to raise the temp by 50 degrees. So as quoted figures are for a 35 degree rise then is it reasonable for the flow rate to half to cope with that extra 15 degrees?

 

[FlyingFish]

Have you tried adjusting the flow rate at the flow switch?

 

[NigelCollins]

Hi 'FlyingFish' No I haven't as I have boiler serviced yearly and have assumed that this would have been set to an optimum level? Also if I increase this isn't temperature likely to reduce?

I had assumed that when we moved here 7 years ago from a traditional boiler and hot water tank that I was never going to get great flow rates to match from a combi but a friend pointed out that the flow rate from his boiler was much greater.....

 

[FlyingFish]

I've no idea what your service chap does, but your saying that you are only getting 7 l/m so your boiler will most likely be modulating down to the required temperature set on the fascia. Thus you are not using the full capability of your boiler.

You need to adjust/increase the flow rate to a level that does not go beyond what the boiler is capable of heating, without the boiler modulating. So max burn while drawing off water at an acceptable temperature and flow rate for this time of year

Page 24 Fig 34 of your installation book.

Apart from adjusting the flow switch, it could be debris in the strainer, or a restriction in the iso valve, or an issue getting the flow to the boiler.

Mick

 

[NigelCollins]

Thanks Mick - will have a look tomorrow

 

[NigelCollins]

Hi Mick - have had a look and I cant work what its set to. Also I can adjust it (anticlockwise) to increase the flow rate but how do I tell if the boiler is modulating? Not too much of an issue as I can always call out Worcester Bosch as I'm paying for a service plan and get them to do it.

 

[FlyingFish]

Open a bath tap (hot) fully then turn the flow rate down at the boiler until the temp of the water is at an acceptable temperature or until you hear the speed of the boiler/fan slow down, and that's it......In simple terms

 

[NigelCollins]

An Update - Worcester Bosch engineer has checked the system and informed me that the flow rate was set to maximum - he agreed flow rate was down to about 7 l/m (with main at 14 l/m) but suggested more likely to be calcium in the hot water pipes reducing the diameter and impeding flow rate? The house was built in the 1930's and I have no idea what has been replaced. We have been here for 8 years and haven't had any of the main hot water feeds through the house replaced.

 

[Dan Robinson]

suggested more likely to be calcium in the hot water pipes reducing the diameter and impeding flow rate? The house was built in the 1930's and I have no idea

Total bolloocks.

 

[Gasguru]

Was the inlet strainer in the boiler pulled out and checked?
What's the cold water flowrate like?

 

[NigelCollins]

Hi Gasguru, not sure if the inlet strainer was pulled out and checked. Cold water flow rate is fine at around 15 l/m

 

[Agile]

A cold flow rate of 15li/min measured as an open pipe flow rate is nice to kow but not an indication of the flow rate you will get from the hot.

The hot water has to go through the boiler and the hot taps and shower.

Typically that is about half f the open pipe flow rate.

It may be the cold supply into the house is restricted on a valve not fully opened. Or it is just a poor flow/pressure available.

It needs properly checking to see what the limitation is and then perhaps to replace the mains supply pipe from the street!

Tony

 

[Gasguru]

You could connect the filling link across to the hot pipework under the boiler to prove one way or the other whether it's "scale" or a boiler fault.
7 litres/min might be just acceptable for a slow shower but bath filling is hopeless.