Worcester 24cdi combi hot water to shower

warehouseman · 8 Aug 2010

Having an intermittent problem with hot water to shower . Occasionally, after someone has had their shower perfectly OK, the next person who has a shower is unable to get hot water, as the boiler fails to ignite. Taps do not work either. Only happens very occasionally but I think it more often happens if someone has taken a lengthy shower say taking 10/15 minutes. Sometimes the next person has to wait 15 / 30 minutes before it seems to reset itself, & then it works perfectly OK again. I'm wondering if this is a case of overheating or an over sensitive sensor of some sort.
Secondly, can anyone explain the purpose of the 'temperature control knob for hot water' on the front of the boiler. Its presently on 'max'(4) but can be turned back to 3,2, or 1. Surely you can adjust the heat of the water by the rate of flow from the taps. Should it be on max? The shower by the way is a straightforward 'new team ' shower.

m1key00 · 8 Aug 2010

It would be very unusual for this boiler to "reset" itself, more likely is that you have an intermittant fault with the hot water demand, have a look under the boiler on the brass diverter valve, there is a pin in the middle with a black button on which when the tap is opened pushes out and on to a microswitch to turn on the boiler for the hot water. Make sure that this pin is being pushed out and that the switch is being made. If not a new diaphragm is required, or if the pin is coming out but not quite making contact with the switch, a small washer can be glued to the black button as a temporary measure. Hope this makes sense. Mike.

warehouseman · 9 Aug 2010

Thanks , I will look. It always seems to happen after a lengthy shower which is why i was thinking it might be overheating. Only happens about once a week but , as I said, seems ok again after about 10/20 minutes.

warehouseman · 11 Aug 2010

As I'm no expert I got in BritGas under our service agreement. Oh Dear! Two lads turned up who, even without looking, dimissed the idea of a valve or diaphragm fault. Said the fault would occur more often if it was this.
Instead they couldn't fathom it out. Asked if my tenants knew how to fluctuate the shower temp !!! (they or me are not stupid) or if there was a pre-pay meter !!
I repeated what the fault was all about. 98% of time all is fine. Once every week or so after 10/15mins of h/w flow, the shower is turned off. The next person 5 minutes later gets in and there is no hot water provision. Try taps, no hot water(radiators stay cold). Wait 20 minutes, all is fine again. The boiler simply doesn't fire up when this fault occurs.
Anyway, they identified that this area is high pressure water (which i knew anyway and the boiler has been fine for 8 years at this pressure)
They reduced the water flow rate from apparently 23litres per min to 13 litres per minute saying this should slightly increase the water temp. Isn't that a pointless exercise if the boiler doesn't come on in the first place.
I left the house after the meeting very frustrated, wondering why I had wasted my morning. Is it just me ?

OLLIE20 · 11 Aug 2010

Its just you, what can you seriously expect them 2 do? You said yourself it happens maybe once a week, do you know how common it is for people, especially tenants not to know how to work things prperly, any decent engineer will ask you all sorts of question about a fault, because you as the cust generally has the answer we need in your info, if your info is correct, which your seems not to be, usually if this boiler locks out it usually displays a flahing red light on the front, which you have to manually reset, depending on flash sequence, it will point in general direction, also would you bother to call someone in you didnt have a repair cover contract? I doubt it, not 4 a 15min fault that doesnt even seem to happen once a week

warehouseman · 11 Aug 2010

Harsh comments but I see your point about tenant situations where conflicting info is given!!
I was just venting some frustation! Such infrequent occurrences must be a nightmare for an engineer.
3 separate people at different times have told me that they didnt see flashing. (I have all the fault flow charts from the original commissioning & have used them before for resetting / & digistat probs years ago) . Each time they seem to remember the water demand light coming on but the water ignite light remaining off. Next time I will race round & witness myself !!

OLLIE20 · 11 Aug 2010

didnt think it was that harsh, however is the truth, if the water deman light is coming on it would seem your diaphragm and microswitch are ok, this should send a msg via PCB to the APS/ Fan to begin ignition sequence, if not for an air flow fault you get a 5 times a second flashing light, (i think) cant remember 100% without looking, if Aps and fan ok should spark at electrodes and light burner if not it should show a flame failue fault, cant remember light sequence for that

nickso · 11 Aug 2010

this sounds awfully like the situations BG get accused of parts changing.

tenant/landlord get fed up of a random and virtually unfixable problem by normal methods so call in BG on contract several times. in an effort to get rid of the recall nightmare the BG chap will change random parts, either with an educated guess or not, until it goes away.

if the landlord was paying for each visit it would get ignored until it broke down proper.

TBH if i had turned up to that job and was told it broke down once in 20 times or whatever i would check everything and leave without changing anything that wasn't faulty there and then.

some customers really need to get a grip on whats actually possible for an engineer to do in situatiosn like that. particularly where the tenant isn't even certain what lights are on/off at the time.

warehouseman · 11 Aug 2010

Thanks Ollie . Out of interest, I know the performance of the 24cdi has a DHW flow rate of 9.5 litres per minute. The Engineer said the pressure from the mains was very strong and that he reduced the 'Water flow' from 23 L per min to about 12/13L per minute.
What does this actually mean & what affect does it have on temperature /pressure from taps etc
Also, I know this sounds silly, but what is the purpose of the DHW temperature control knob, bearing in mind that every engineer I've ever seen says just keep it at max. why have adjustable levels 1/2/3/max ?

warehouseman · 11 Aug 2010

Nickso. I know it sounds like that but I really am not that sort of chap.Very much an 'amateur' landlord, trying do do whats best. I was very reluctant to call out anyone.I've had a BG contract for 10 years & can only recollect calling them out twice - once a digistat problem and secondly a radiator leak ! I only wanted to sort before other person arrived. I know 'Landlords' have rubbish reputations but I assure you I'm not that type

nickso · 11 Aug 2010

i didn't mean that you necessarily are that type of landlord. you did seem to be a bit ****ed off they didn't fix anything without thinking about why though.

as regards flow rate. why he would leave it at 13 l/m when the boiler is only rated to run at 9.5 for max water temp boggles the mind. off the top of my head the cdi lists 9.5 l/m and 12 l/m as acceptable flow rates. i always advise a customer to go with the lower rate as it makes a big difference in winter.

a 24kw 24cdi can only heat the incoming mains water to 40 degrees over the mains temperature at 9.5 l/m. if the mains comes in at 5c then the boiler can only heat it to 45c...at 9.5 l/m. increase the flow rate to 12 l/m and it can only heat 35c above mains temp....a mere 40c at the tap. if the mains temp goes down so does the hot tap temp. i lost count of the calls i had last winter to 24kw boilers where the incoming mains was as low as 2c and the hot temp was dipping to 35c at the tap....no fault of the boiler, its just not big enough to cope.

remember also if the boiler is in generally poor condition you can often knock a couple of degrees off....blocked heat exchangers and the like will all affect temps.

warehouseman · 11 Aug 2010

Thanks Nickso for explaining it. Why the flow rate was so much higher at 23 is anyone's guess then. That must have impacted quite a lot on performance.

Any ideas on the other point about The DHW control knob. Always at max. Is that just maximising the rate of speed to the taps cos why bother have an adjustable knob !!

nickso · 11 Aug 2010

i doubt it ever ran at 23 l/m. not at a kitchen tap anyway. anything above 18 l/m is likely to be spray city at any tap other than the bath tap, i doubt many would be foolish enough to use it at 23 l/m unless they want to wash the floor without a bucket.

regarding the temp knob. all that does is limit the temp to the hot tap. in effect it reduces the gas used at the gas valve and sets a lower max temp in relation to the flow rate ( laymans terms before any RGI's start sniffing). if it is set to 9.5 l/m and the incoming mains is at say 8c it will heat to 48c....getting uncomfortable for some and it will get a lot higher if flow rate is reduced futher.

most 24kw boilers will be set to max in this country because they are pretty underpowered for our mains temps in the winter, in the summer some of my customers will turn the temp knob down a notch to compensate for higher incoming mains temp.

personal preference in the end.

OLLIE20 · 11 Aug 2010

warehouseman said:
Thanks Nickso for explaining it. Why the flow rate was so much higher at 23 is anyone's guess then. That must have impacted quite a lot on performance.

Any ideas on the other point about The DHW control knob. Always at max. Is that just maximising the rate of speed to the taps cos why bother have an adjustable knob !!

The higher the knob the hotter the water, it will make the thermistor (temp sensor)/ PCB modulate the gas down sooner so as to keep water at lower temp, people tend to use this option more when they have young kids n that, usually most whacked up at full, no worries though

warehouseman · 11 Aug 2010

Believe Nickso, that flow rate was pretty high because anyone turning the kitchen taps on for the first time got soaked. I did and just thought it a naturally high pressure.
Many thanks to you & Ollie for making things much clearer.
I'll keep you posted on the annoying intermittent thing.

diynot

If you need to find a tradesperson to get your job done, please try our local search below, or if you are doing it yourself you can find suppliers local to you.

Select the supplier or trade you require, enter your location to begin your search.

Are you a trade or supplier? You can create your listing free at DIYnot Local

Worcester 24cdi combi hot water to shower

Similar threads