boiler

[bippih]

Hope someone can help,l have a problem with my boiler,its a bosch worcester 24 cdi bf.The central heating works ok.When l open the tap for hot water about half way the teperature is ok,but when l open it full bore the temperature drops off .Any ideas!

 

[ollski]

should imagine you're asking it to heat a greater volume of water than it is capable of....a combi can only supply a certain flow rate of water at a 35 degree temperature rise above the incoming mains water. Check your instructions for what that is then measure your temperaure rise between the hot and cold taps at the flow rate indicated in the instructions.

 

[PEDANTICVINDICTIVEMAN]

Has it always done this since new or just start doing it ?. 24Cdi has a built in restrictor so tap should be able to be full on and water hot enough.

 

[ollski]

Has it always done this since new or just start doing it ?. 24Cdi has a built in restrictor so tap should be able to be full on and water hot enough.

You can remove them though can't you pvm?

 

[cross thread]

WATER RATE SHOULD BE ABOUT 10LTS PER MIN AND THIS SHOULD GIVE A 35 DEG TEMP RISE IF EVERYTHING ELSE IS RIGHT,GAS RATE ETC, THAT IS ALL YOU BOILER CAN DELIVER

MOD

see 6

 

[chrishutt]

Gordongas, MOD is trying to tell you to stop SHOUTING!

 

[ChrisR]

WATER RATE SHOULD BE ABOUT 10LTS PER MIN

They set it to about 8 litres/min to get a higher temp rise - needed for a bath in the winter. It does sound like it's been removed though.

 

[bippih]

Has it always done this since new or just start doing it ?. 24Cdi has a built in restrictor so tap should be able to be full on and water hot enough.

its just started doing it

+++++++++++++++++++++++++++++++++++++++

Has it always done this since new or just start doing it ?. 24Cdi has a built in restrictor so tap should be able to be full on and water hot enough.

No its just started doing it.Could it be anything to do with any of the thermisters.

++++++++++++++++++++++++++++++++++++++++

should imagine you're asking it to heat a greater volume of water than it is capable of....a combi can only supply a certain flow rate of water at a 35 degree temperature rise above the incoming mains water. Check your instructions for what that is then measure your temperaure rise between the hot and cold taps at the flow rate indicated in the i
nstructi
ons.

The boiler has worked ok for the last five years,its just started doing it

________________________
moderator

please note 10a which is here

 

[COG]

The 9 LTR flow restrictor fitted is made up of three parts ,an outer ring an inner ring usually colour coded and a specific size and an "o" ring between them ,the "o" ring can perish and fall away almost doubling the flow rate on the other hand you gas pressure could have dropped.
PS no combi will give a temp rise of 35 deg C at full flow, that would be no good BUT they will all quote a 35 deg rise and a specific flow rate so you can compare one against the other the higher the flow rate the better the combi

 

[bippih]

Thanks for the advice,is the restrictor on the outlet pipe from the water to water heat exchanger.If its not the restrictor does that mean the gas valve pressure needs adjusting or is the gas valve faulty?

 

[COG]

The restrictor is on the inlet to the plate heat exchanger at the back of the plate on the connection from the div valve . time your flow rate ie it should fill a 1 gallon / 4.5 ltr bucket in 30 seconds or 1 ltr in 6.6 seconds.
To test the gas you will need a corgi card and a manometer or give details of your gas meter ie is it dials or digital cu feet or cu M , then you can time it over to see if it is giveing full gas at full flow (gas rate)

 

[bippih]

The flow rate checks out ok,1ltr in 6seconds.The gas meter is not digital,so l assume it is dials and is measured in cubic feet .How would l measure the rate.

 

[chrishutt]

Measure the time it takes for the red pointer on the main dial to revolve one complete revolution (1 cu. ft.). Then post that figure here. The time should be something like 36 seconds to pass the gas to produce 30 kW of input.

 

[bippih]

With the hot water tap open full bore,it took 96 seconds for 1cu ft.

 

[chrishutt]

Could be that the burners were modulating down. 96 seconds represents a heat input of only 11.5 kW. Perhaps you could repeat the test with at least two hot taps open to maximise burner gas consumption.