Increasing DHW flow rate by changing PRV?

[thedman]

Hi,

I have a combi boiler (glow worm xtrafast 96) (mains fed) and the hot water flow rate is poor. The cold water flow rate is fine on all taps, inside and out.
There is a Caleffi (model number 533641, I believe) PRV before the boiler, this is marked and sealed at 3 bar.

If I were to increase the pressure on the PRV, would it safely increase my flow rate???

I say "safely" because my boiler manual says "Maximum Service Pressure 3 Bar" for heating but for "maximum supply pressure" for hot water it says 8 bar. So whilst my DHW can handle 8 bar, would I blow up my heating by increasing the cold supply above 3??? Or have I misunderstood "Maximum service pressure"?

Cheers in advance,

Dave.

 

[Mike Jackson]

The restriction is your boiler not the PRV. You will get a good flow rate at 3 bar if the boiler is big enough. Your boiler will only give you 11.3 l/min.

 

[mountainman]

The PRV is a safety device, don't fiddle with it.

 

[thedman]

So does it then limit the incoming cold to the Max service pressure?

 

[kirkgas]

hi,

i have a combi boiler (glow worm xtrafast 96) (mains fed) and the hot water flow rate is poor. The cold water flow rate is fine on all taps, inside and out.
There is a caleffi (model number 533641, i believe) prv before the boiler, this is marked and sealed at 3 bar.

If i were to increase the pressure on the prv, would it safely increase my flow rate???

I say "safely" because my boiler manual says "maximum service pressure 3 bar" for heating but for "maximum supply pressure" for hot water it says 8 bar. So whilst my dhw can handle 8 bar, would i blow up my heating by increasing the cold supply above 3??? Or have i misunderstood "maximum service pressure"?

Cheers in advance,

dave.

do your family and neighbours a favour "step away from the boiler"

 

[mountainman]

Ah! I'm probably mistaken, a PRV in my world is a Pressure Relief Valve (overpressure safety device)
I suspect that you are referring to a Pressure Reducing Valve, something entirely different.
I refer you to Mike's excellent advice in an earlier post.

 

[thedman]

Yeah, sorry should have clarified, Pressure Reducing valve.

 

[GQuigley67]

you cant change the DHW flow rate on the boiler it is set at that so the boiler can heat the water if it was more you wouldnt get hot water if it was less it would be scalding

 

[jtsplumbing]

May need cold water filter cleaning out !

 

[thedman]

Good point! Thanks, I'll try it.

 

[Ruski]

Sorry to jump on board - but is there a filter on ALL combis cold in?

 

[mountainman]

Sorry to jump on board - but is there a filter on ALL combis cold in?

Generally yes, but sometimes they are not fitted.
Depends on the installer.

 

[Ruski]

Cheers MM - learn summat new every day!!

Cleaned as part of a service normally or just ignored until it causes a problem??

 

[thedman]

The cold flow rate is 10.5 l per min and the hot flow rate is 4.52 l per min regardless of what temp the hot water is set at. However I have just noticed the stopcock going in to the boiler...... Should I open this more??? I've already tried but it has seized up...

 

[stevetheplumber]

The cold flow rate is 10.5 l per min and the hot flow rate is 4.52 l per min regardless of what temp the hot water is set at. However I have just noticed the stopcock going in to the boiler...... Should I open this more??? I've already tried but it has seized up...

sounds like youve found the problem

 

[Ruski]

Try closing it (the stopcock) a little before trying to open it up - sometimes helps.... But I'm not responsible if it makes the flow worse!!!!