Worcester Heatslave 9.24BF

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MarkGibson

Can somebody give me some help.

I have a boiler of the above type and works fine on central heating, it will happily chugg away all day etc.

However my hot water is causing me a problem, it will run for about 10-15 mins providing hot water, however after this time the whole boiler shuts down (pilot light goes off etc) it almost seems like it is overheating. (and just before this happens the water gets extremely hot)
And is cutting out on high water temp. Now I don't think it could be the gas valve becuase wouldn't' the problem be shown on the central heating aswell?
Also how does the maximum hot water temp work, does the hot water side have a thermostat or does it just work on the time taken for the water to flow through the heat exchanger?

Any help would be greatly appreciated

Mark
 
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the dhw has a thermister (non adjustable thermostat) screwed into the dhw outlet pipe of the secondary heat exchanger. it will have 2 red wires going to it. from what you've described it's likely that this is your problem. they are easily changed with the cold supply to the boiler switched off but awkward as hell if the installer didn't give thought to allowing room for the control panel to lower.
 
M

MarkGibson

Thank you very much for your swift reply.

I have ordered the part.

Dont mean to be a paiin but could you explain how the heat exchanger side of things works?

Regards

Mark
 
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in dhw mode
the boiler fires the burner which directly heats primary water (the same stuff as what's going through yer rads)in the main heat exchanger . this heated water is pumped into a secondary heat exchanger via a diverter valve that sends it there, instead of your ch system. this secondary heat exchanger has a coil of pipe running through it. within this coil is your incoming cold water which, by passing through a vessel full of heated water picks up the heat indirectly, i.e. the two sets of water don't mix. the outgoing dhw heat is passed across a NTC (negative temperature coefficient)sensor or thermistor. this small sensor will lower the resistance through itself as it gets hotter and in turn this resistance will tell the pcb to reduce the amount of gas being burnt. as the water slightly cools it will tell the pcb to increase the gas. if your thermistor isn't reacting to the temperature change then it won't tell the pcb to reduce the gas and the boiler will overheat. there is the chance that scaling/fouling of the secondary heat ex means that the dhw water never heats up enough to tell the thermistor to reduce the gas. if this is the case then the primary water would still remain very hot and cause the boiler to overheat but it wouldn't be the thermistors fault. a very crude test of a blocked/fouled/scaled heat ex is to fire the boiler for dhw, with one hand feel the outgoing dhw pipe with the other feel how hot the vessel is. if the vessel is jumping hot but the dhw pipe is cool it could be a heat ex problem. this test would depend on your dhw not running too fast at the taps (fill a pint jug in about 3-4 seconds)



i think that's covered everything.
 
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Question for weargas - I have a Highflow 3.5 bf with the same symptoms - is it the same solution (where is the thermistor located) - also while the water is heating before cutting out , there is a droning noise ?

Thanks in advance
 
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mike_j said:
Question for weargas - I have a Highflow 3.5 bf with the same symptoms - is it the same solution (where is the thermistor located) - also while the water is heating before cutting out , there is a droning noise ?

Thanks in advance

sorry mike,
very little dealings with the highflow 3.5 bf, not many installed in the north east. I'll have to leave you with someone who's a little more experienced with that model, any advice i give may be misleading which is worse than it being wrong. i'm sure one of the regulars could help you. start your own thread about the problem.
 

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The DHW mode that Weargas described is spot on for the 9.24 but the 3.5 highflow uses thermostats and a non modulateing gas valve (two settings, high for dhw and pre set for ch ).instead of heating the primary water directly as in the 9.24 it stores it in the heat bank on the left of the boiler at the temperature you have set the stat to.between 54 and 82degC. you could well have a scalr problem as above but the noise you describr is the gas to water heat exchanger getting to hot and vibrateing and on the 3.5 it could be a loss of circulation on a number of things all too tricky to test without a good surface temp probe.
 
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Thanks COG - how can I descale or should I be looking to get worcestet engineer in
 

COG

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If you need to de-scale its easy, hire a descaleing machine from your hire shop with chemicals conect to the hot and cold inlet and outlet of the boiler (cut the pipes and fit a couple of isolateing valves).then run the machine for upto one hour reversing the flow of the pump every 15 mins. are you in a hard water area. ps a de-scaleing machine is basicaly a small powerflushing machine mine cost £150. so it cant me much to hire
 
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Hi,

This is most likely to be directed at weargas....sorry mate but you seem to have a wealth of knowlege on the Worcester Heatslave 9.24.

I need some help as follows: -

My central heating works very well, controlled via a Honeywell room thermostat in our hallway ( 2 bedroom semi) we have 7 radiators in all of which are bled regularly.

We have had some trouble with the hot water supply via the combi boiler over the winter months, most probably due to half of the radiators being removed for decorating purposes etc.

Now I have all radiators back on and bled, I have installed a mixer shower.

My problem is, before we installed the shower, be had to use a hand held cheap shower head which connected to the bath taps via the flexible pvc/ rubber connectors. The hot water supply never really got hot enough until the flow was reduced majorly to a 'trickle'. Now I have the shower installed, the problem still remains and as before I get the occasional groaning of the boiler complete with brief loss of hot water supply.

I have noticed also that I have water leakage (approx 1/2 litre per week) coming from perhaps a valve or fitting from within the boiler. Can you digest this information and give me any pointers/ suggestions etc.

Also are parts still readily available for this model of combi boiler as I have tried to start an insurance policy via british gas and they tell me they cannot repair if it fails.

I would obviously like to have the boiler serviced if it will still do a job. However if it cannot succesfully feed a shower then I will need a new boiler. Can you recommend a decent model on a budget.

Many thanks in advance :D
 

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