Low flow rate from combi boiler

Bluefox_2

I've recently bought a house with a Biasi combi boiler. The central heating works fine but when I turn on any hot tap the flows starts off OK but then quickly slows to something very feeble - useless for filling a bath. I asked a plumber to look at it but he could not find anything obvious that was wrong with the boiler. The flow rate is the same irrespective of whether the heating is on or not. Flow and pressure on the cold water is fine.
Any ideas what might be wrong?

Skiduck

what flow rate do you have, do you know?
Combi's (especially older ones) generally have poor flow rates - I think the Biasi range is round about 9 or 10 if you are lucky.

Bluefox_2

The boiler is 4-5 years old. I haven't measured the flow rate and I am not there at the moment, so can't. What are the units? Litres per minute?

Skiduck

yep litres per minute

Bluefox_2

I would guess the that the flow is roughly 2-3 nowhere near 9-10

Skiduck

I've checked with Biasi and there are 3 components to check if you have reduced flow rate.
1. DHW Circuit
2.Heat exchanger
3. DHW Filter
If it is the heat exchanger, I would say goodbye to the boiler and look at getting a condensing combi.
Do you have any scale inhibitors on the circuit and how is your local water hardness?

Bluefox_2

The plumber who looked at it examined the heat exchanger and said it was OK. Only recently acquired the house so I don't know about scale inhibitors. I think the water is fairly soft, based on lathering. It is certainly a lot softer than Kent, which is what I am used to.
Thanks for your help

whitebeams

It seems strange that it starts off ok and then the flow reduces almost as though once the flow starts a bit of crap is pushed against the filter which reduces the flow. Did the plumber take the heat exchanger out of the boiler to examine it?.......Brian

Bluefox_2

Yes, I wasn't there at the time but he said he removed the heat exchanger to check it. I think he also said he immersed it in a solution to remove any lime deposits

Bluefox_2

One of the main reasons I am concerned about the flow rate is that I want to install a shower. If flow is likely to be a problem with this type of boiler then I will opt for an electric shower, but I would rather not