cold water flow rate vs hot water flow rate

[nicksterz]

Hopefully someone can shed some light on my problem.

I've got a Keston C36 combi boiler in my 2 bedroom flat. The boiler is sensing that the DHW flow rate is ~2.5 liters/min which is on the borderline hence the doesn't fire up at times. This is happening at all the hot water taps in the flat (i've clean the aerator on all of them). The static water pressure is coming in at 3 bars while the cold water flow rate is ~9 liters/min. So my questions

1. Is it normal to have such a big difference between cold and hot water flow rates?
2. Any ideas what could be wrong?

 

[DanTheGas]

The C36 should go down to about 0.4 l/min from memory and function correctly (If there's any such thing as a fully functional c36 after a few days of operation).

There is a small 1/2" filter fitted internally to the appliance on the water service pipe work which could be the cause of the loss, but you should really use a registered engineer to get this cleaned and preferably someone that knows about Kestons as these can be very problematic boilers.

 

[ALEC1]

apart from what has been said, no doubt you have some fancy taps that operate at much higher pressures...

 

[Madrab]

Has this just recently started and was there any work done on your cold water piping? Is there an isolator /stop tap on the cold water inlet pipe to the boiler? Is this fully open?

 

[nicksterz]

The C36 should go down to about 0.4 l/min from memory and function correctly (If there's any such thing as a fully functional c36 after a few days of operation).

There is a small 1/2" filter fitted internally to the appliance on the water service pipe work which could be the cause of the loss, but you should really use a registered engineer to get this cleaned and preferably someone that knows about Kestons as these can be very problematic boilers.

Thanks, will get someone to check on that. On the manual of the C36, it says that flow rates of <2.5 liters/min tru the boiler will not trigger a demand. Which seems to be true in my case

Has this just recently started and was there any work done on your cold water piping? Is there an isolator /stop tap on the cold water inlet pipe to the boiler? Is this fully open?

I just moved in last year and this has gradually been happening. Nothing has been done as far as i'm aware of to any of the piping and yes i've double, triple checked the stop tap from the mains into the boiler, it is fully open

One more thing i wanted to add, was curious about the cold water flow rate directly from the mains so checked it this morning and to my surprise, that was about 20 liters/min but from any of the cold taps, i'm only getting ~9 liters/min I'm in a new-ish flat, < 5 years from new built so i wouldn't think it be limescale in the pipes could it?

 

[Madrab]

Sounds like you have a pressure regulator fitted somewhere or a stop tap/isolator partially closed. How did you test the mains was 20Ltrs/min outwith running a tap?

 

[nicksterz]

Yup there is a 3bar pressure reducing valve right after the mains. Have checked that (took it apart, no debris or blockage). I tested the flow from the filing loop as that what right after the reducing valve and right before the cold water feed into the boiler. Can't figure out why with that pressure and flow rate i'm only getting 9 l/min of cold water from the taps and worse, the hot water flow rate through the boiler is only ~2.5 l/min causing the boiler not to sense the demand