Joined: 31 May 2009 Posts: 23 Location: United Kingdom Thanked: 1 time
Posted: Wed Nov 04, 2009 9:45 pm Post Subject:
Worcester 40 CDi - Fault
Evening all...Bit long winded this, i'll be as brief as possible.
Recently installed 40CDi on an existing powerflushed open vented system, 28mm boiler F&R to pump & controls approx 6m from boiler. On demand boiler fires briefly (2-3secs) before displaying a hydraulic fault symbol (opposite corners flashing on and off with flow temp). This mode begins with the flow temp as low as 22deg and continues for approx 45mins at which point the boiler usually fires up properly...Worcs came out and ok'd the appliance and pointed the finger at the pump, we upgraded the pump from a 15/60 to a 25/55 and problem persists on all 3 pump speed settings. When boiler is in high fire all 25 rads kick in nicely and I am as sure as I can be that there is not a circulation problem.
No other error codes are being displayed and all I am getting from Worcs Tech is "...it's not a boiler fault..."
Any thoughts would be gratefully recieved, thanks in advance Mark.
Evening all...Bit long winded this, i'll be as brief as possible.
Recently installed 40CDi on an existing powerflushed open vented system, 28mm boiler F&R to pump & controls approx 6m from boiler. On demand boiler fires briefly (2-3secs) before displaying a hydraulic fault symbol (opposite corners flashing on and off with flow temp). This mode begins with the flow temp as low as 22deg and continues for approx 45mins at which point the boiler usually fires up properly...Worcs came out and ok'd the appliance and pointed the finger at the pump, we upgraded the pump from a 15/60 to a 25/55 and problem persists on all 3 pump speed settings. When boiler is in high fire all 25 rads kick in nicely and I am as sure as I can be that there is not a circulation problem.
No other error codes are being displayed and all I am getting from Worcs Tech is "...it's not a boiler fault..."
Any thoughts would be gratefully recieved, thanks in advance Mark.
The fault you are describing is the gradiant limitation kicking in, boiler flow temp is rising to quickly.
How is your system set up? is the heating split into zones? is it two or three port zone valves that are used? Is there a system by-pass fitted?
While you are here, whats the official name and cause of the [ ] symbol?
Are you in the CC yet?
That symbol is the syphon-fill Tony. When the boiler fires from new it first goes through an 8 minute air purge as there is no AAV on the heat exchanger. This is a one time only function however it can be turned on in service mode if required.
After that the boiler then goes into syphon-fill where it fires at low rate for 15mins to fill the trap.
every time power is interupted to the boiler ie spur or on off switch are switched off but not after boiler re-set it will go through syphon-fill before returning to normal operation.
That is not the symbol he is describing though, the symol he is describing is similar, [] imagine that but cut in half on the top left you have half that symbol and on the bottom right you have half that symbol.
I suspect it's low flow on start up or boiler needs to be rated.
Joined: 31 May 2009 Posts: 23 Location: United Kingdom Thanked: 1 time
Posted: Thu Nov 05, 2009 5:52 pm Post Subject:
The system is set up as follows: Grundfos 25/55, 22mm auto by-pass and then 3no. 22mm 2 port valves, one for the HW and the other two for the two 22mm heating circuits. Although there are two 22mm heating circuits they act as one zone and the two 22mm heating zone valves operate simultaneously.
When I set the boiler to max via the boost button it takes 7 minutes for the flow temp to rise from 30deg to 70deg (fault symbol still displayed during this mode).
The system only needs about 35kw but when I suggested down rating the boiler to the Worcs Tech bloke he didn't seem over impressed.
When I set the boiler to max via the boost button it takes 7 minutes for the flow temp to rise from 30deg to 70deg
That does not sound right.
What is the total output of the rads roughly?
If you allocate an average of 10L per kW for rads plus pipework, it should take around 25 minutes to go form 30C to 70C.
30CDI would have done nicely methinks, but never mind, the 40 is there now.
40 kW capacity heats about 14 litres of water 40 degrees in 1 minute. That would lead to 100 litres in 7 minutes if I have my tables right, IF no heat was lost. As there clearly is heat dissipating through the rads, you are left with an estimated 80 - 90 litres that would have been heated up 40 degrees whilst circulating through the rads. Ball park figures obviously. I don't see how 29 kW worth of rads plus the pipework for it could be as little as that.
Q1: did ALL the rads get FULLY hot in that 7 minute span?
Q2: did you gasrate the boiler?
Q3: were all the lockshields wide open?
Q4: was the dhw side closed?
Q5: why didn't you post this in the CC?
Q6: why did you stick a 40kW boiler in on 29 kW of rads?
Q7: did you adjust the rad output to steamer settings?
Joined: 31 May 2009 Posts: 23 Location: United Kingdom Thanked: 1 time
Posted: Thu Nov 05, 2009 10:28 pm Post Subject:
Q1: did all rads get fully hot in that 7min span?
A1: I was concentrating on timing the temp rise so I didn't check.
Q2: did you gas rate the boiler?
A2: 43kw net
Q3: were all the lockshields wide open
A3: no - some, not many, have been turned down.
Q4: was he dhw side closed?
A4: yes
Q5: why didn't you post this in the CC?
A5: wasn't aware of it until now...I assume that this is the CC that Agile was referring to...
Q6: why did you stick a 40kw boiler in on 29kw of rads?
A6: was thinking 29kw heating, 3kw dhw plus 10% for pipe work. Thought I might have been chancing it with the 30 as the client was making a lot of noise about the old boiler not being man enough.
Q7: did you adjust the rad output to steamer settings?
A7: have I got a 20deg differential across the F&R?...no
Q3: were all the lockshields wide open
A3: no - some, not many, have been turned down.
To get rid of the fault "code" during the installation/commisionning, open them relatively wide, e.g. 7-10C drop.
Q6: why did you stick a 40kw boiler in on 29kw of rads?
A6: was thinking 29kw heating, 3kw dhw plus 10% for pipe work.
Modern, high recovery/ high insulation cylinders should be time separate from the ch. They are generally between 10 and 20 kW, so no point adding 3 to the boiler load.
10% for the pipes?
Q7: did you adjust the rad output to steamer settings?
A7: have I got a 20deg differential across the F&R?...no
I actually meant if you stuck to the capacity as given by the manufacturer, which is 10 - 15 % more than you actually get on a steamer. In other words: if the table says: 1789 Watt, 1500 - 1600 out of it with a boiler in condensing mode. The result of that would be that the rads that you counted as 29 kW, will only dissipate 25 kW with the new boiler.
It shouldn't be a problem as the boiler will modulate down to about 15 kW.
The boiler is not running too high, so it seems to be a matter of too little flow. Pump is easily big enough, so it must be a restriction somewhere.
Manual bypass somewhere?
"Balance valve" partially shut?
Some numpty that installed a loop?
Limescale/magnetite lump somewhere?
Joined: 31 May 2009 Posts: 23 Location: United Kingdom Thanked: 1 time
Posted: Thu Nov 05, 2009 11:19 pm Post Subject:
Rads appear to be piped properly albeit in 10mm, not via a common manifold but each teeing into the heating circuit individually...Each rad was flushed seperately and the machine has a pair of magnets so I could see how the flush was going. Used 4 litres of X800.
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