dhw flow

[columbo]

hey guys how do? I have a quick question about hot water v cold water flow. the boiler is a Worcester bosch 240 combi. so I have done a flow test at kitchen taps to begin with which worked out like so. hot tap=6.9litres min/ cold tap=11.3litres min. boiler is about a metre from sink btw. so what do you guys think of the flow difference between the hot and cold? would you say there is a restriction in the hot flow? any help would be much appreciated:smile5:

 

[jtsplumbing]

A old Worcester 240 will give about 8 lts your getting about 7 lts allowing for minor restrictions (dirt in heat exchanger etc.) and age of boiler your doing pretty good, What is temperature like ?

 

[columbo]

now the temperature is another story which is actually the main issue. had the bathroom hot tap about half open for a few minutes the other day and took a max temp reading of 76.3 degrees. kitchen hot tap went to 72 degrees. and shower temp fluctuates a lot. would I be right in thinking that the boiler should automatically modulate the gas pressure to coincide with the hot water flow to keep temp to around 60 degrees?

 

[spanner]

Sorry. But we can't be giving out any information whatsoever on technical issues if you aren't GSR .

Unfortunately.

 

[newcastle phill]

Depends on the boiler.
Refer to manufacturer data for the make and model.

Some old ones modulated in 2 steps. Modern ones can throttle alot more.

 

[jonnyswamp]

Thats quite an old boiler with not a very good flow rate (even from new)
As said above the current flow rate is low, but about what you'd expect
Scale problems can cause what you are describing

 

[columbo]

hi spanner. I am just wanting to know about the general functioning of the boiler as with the shower playing up and the hot water tap going to 76 degrees ( should it not be regulated to about 60 max?). no way I would go near the gas side of things as that is not a risk I am willing to take. cheers

 

[columbo]

hi phill. I found a pdf boiler manual online which matches the one we have (its the one with the automatic ignitor) and according to manual it is fully modulating.

 

[columbo]

hi jonny. in the manual it says 8.5litres min +/-15%. so would the flow comparison result I got cause the issue with the shower fluctuation? any help from you guys would be great cheers.

 

[SilentMike]

Could be a problem with the shower is it thermostatic or manual mixer? could also be a twisted shower hose or dirt partially blocking the head?

 

[columbo]

hi mike. the shower has a pre 91 grey cartridge pressure balanced mira 415 mixer. the other thing is when shower is put to full hot and bathroom sink hot tap is fully opened the shower basically cuts out. any ideas? cheers

 

[jonnyswamp]

Faulty cartridge in shower could cause fluctuation
If you are getting constant temps of 70 degrees + through your taps then it needs looking st by a GSR engineer
If it's only momentarily, it can happen like that on older boilers when the hot tap is first opened
May be worth booking a visit from an eng to make sure thing are right on the gas side of things

 

[columbo]

hey jonny. its not like a fast fluctuation. the temp increases slowly then decreases slowly on its own every few minutes. with the hot tap you can have it full open for about a minute then when you close it down about halfway the temp starts gradually rising to over 70 degrees. what you reckon? cheers

 

[jonnyswamp]

It needs looking at by a GSR
Can't give you any more advice as per forum rules

 

[columbo]

hey guys. I understand about the forum rules. but if someone could answer my question in post 11 I would very much appreciate it? third floor flat btw(if that matters at all) cheers

 

[jonnyswamp]

Your boiler can only supply a given ammount of hot water ie around 8 litres per min
If your shower and basin tap are both on, they would both require around 8 lpm so your boiler would need to supply 16 lpm, water will take the path of least resistance so the lowest outlet will take all the flow and the shower will be starved

 

[jtsplumbing]

You can if you are happy to have a go, is remove shower cartridge and check internal filters may have some dirt in filter, other option try a different shower head , and are you in a hard water area, depending on age of cartridge if your going to strip it down fit new cartridge,

 

[Riley]

Combis are not designed to run two outlets at the same time. The water is probably taking route of least resistance to the tap rather than via the body of the shower

 

[spanner]

This is becoming a no goer
I'm opt out as I've said before.
Merge Christmas and new new year

 

[columbo]

hey guys merry xmas to you all:grin:

 

[columbo]

You can if you are happy to have a go, is remove shower cartridge and check internal filters may have some dirt in filter, other option try a different shower head , and are you in a hard water area, depending on age of cartridge if your going to strip it down fit new cartridge,

so jts I went with your advice about the mixer valve. stripped whole thing right down but there was no sign of any strainers. just spring loaded 1 way valves on each side. catridge also seems to be doing its job. also while the mixer was of I done flow tests on the pipes going to mixer. with cold pipe blocked off I got 8.1 litres/min from hot pipe. and with hot pipe blocked I got 19 litres /min from cold pipe. I also checked the temperature at hot pipe which was going between 50c and 54c. what you guys think of that?

 

[columbo]

yeah I understand what you mean about the path of least resistance jonny and riley.

 

[Riley]

Well point being if you've only got 8 lpm to play with it will never ever run two outlets suitably

 

[Riley]

I'm not quite sure what you're trying to achieve now mate

 

[jtsplumbing]

You will never get the same flow from hot has you do from cold ! hot supply is restricted through boiler, reason boiler is only designed to give 8.5 Lts there is nothing you can do to alter this other than replacing your boiler with one that will give better flow rate, and if you are trying to match cold water then you will need a unvented cylinder / or storage combi both of these are quite expensive options