low hot water flow rate

[fossilbluff]

Hi, I have a vokera linea 28 boiler, we have had it for approx 9 years, and it is always annually serviced.

The hot water flow rate is terrible and must have got this way slowly over time as I cant believe it was initially like this, the cold water rate measured at the kitchen tap is 9 litre/min, and the hot is barely 3 litre/min, which makes running a bath a non event, is this just a fault with the DHW heat exchanger clogging with limescale over the years, or could it be something else. (sometimes when having a shower the temp does go up and down a bit, but we have got a thermostatic controlled tap, if that makes sense), thankyou in advance, Simon.

p.s. the boiler service engineer said if I wanted to increase my flow rate I would need to buy a new boiler, hmmm.

 

[plumman]

Hi there,
9 litres/min coming in is poor,
is your stop tap open fully?
is the in coming main in lead?

If you had a new boiler you would only get about 8 l/m if your lucky.

 

[fossilbluff]

Hi, yes stop tap is fully open, and I think the mains in is plastic then into copper, (The house is only 10 years old). the kitchen/bathroom cold water tap supply seems quite good compared with other houses I have lived in, it's just the hot water ??

 

[jtsplumbing]

If you are in a hard water area more than likley that plate heat exchanger is cloged up, you can remove and descale but better off replaceing, then fit anti scale device on main cold water into boiler,

 

[fossilbluff]

Hi jtsplumbing, thanks for your reply. I take it you mean the DHW heat exchanger (sorry, not totally up on boiler jargon), also i have heard that the flow switch and restrictor (although I can't find that-any ideas?) can get blocked, what do you think, many thanks, Simon

 

[jtsplumbing]

Flow switch only tells boiler that that hot water is required, you could have a partley blocked restrictor (Plastic disc on cold main into boiler) if fitted this just slows down the flow of water into boiler, if your in hard water area ,more than poss that plate heat exchanger is blocked ,easy part to replace.

 

[fossilbluff]

Thanks again for the reply, will have a look for the restrictor, but I think your right and will replace the heat exchanger, thanks, Simon.

 

[southcoastboile]

when you top pressure up on this boiler there is a black lever, if you dont put it back to original position it will restrict flow to hot taps, if its not that then i agree with what others have said

 

[fossilbluff]

I have replaced the dhw heat exchanger, I received a 8037 not a 8036, my mistake but it only seems to a millimetre bigger all round and just needed the insulator jacket trimming, so system is back up and running after a minor leak. but my hot water flow at the kitchen tap has gone from 3L/min to 3.5L/min, not impressed. I must say that when I removed the old heat exchanger it didn't seem that mucky inside ?? still havent found this restrictor disk, but it must have one as my cold water at the tap is 9L/min, ANY IDEAS ???

 

[fixter1]

FLOW RESTRICTOR​

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Disconnect the cold water inlet pipe at the DHWflow switch Using a small screwdriver, gentlyease the flow restrictor from its seating. Replacein the reverse order. Ensure all seals are ingood condition, taking care to ensure they arereplaced correctly.​

 

[fossilbluff]

I will have a look in the morning, just to check, the cold water comes in goes through the filling inlet valve, then through the DHW flow switch then into the DHW heat exchanger, will the flow restrictor be fitted on the inlet to the flow switch, and if I find it should I remove it totally, thanks again, Simon.

 

[AWheating]

9lpm on a 10year old house is poor. Honestly a combi boiler was an incorrect choice for your property. Any engineer that tells you a new combi boiler is whats needed is an idiot.

do you have a water meter inside your house? what taps do you have?(mixer taps are poor on low floe rate and restrict them further) i would get a plumber to test your cold main and measure the dynamic pressure and flow, clean out all filters in water meters, iso valves on boiler, taps, showers if there are any present.

the hot water flow may only be a symptom of poor cold supply.