Ravenheat DHW Question - Newbie!

[dcackers]

Hello all,

I have a question if you wouldnt mind helping with...

I have a Ravenheat CSI85 boiler which has recently stopped producing a continuous flow of hot water.

The boiler fires up but then simply cuts off, and then re-ignites up to 15 seconds later.

I have had a plumber out to look at the situation who has in turn replaced the DHW sensor - to no avail.

I am now faced with buying another part which i'm told 'may' fix the problem.

Using the fault-finder in the Ravenheat manual, it says to replace the Potentiometer, but the plumber seems to think it may be the diaphragm in the 3-way valve (he said there may be holes in it)...

Please can somebody advise which may be the best solution or angle of attack on this situation?

Thank you all very much for your responses.

Daniel

 

[kitch0978]

does your heating work fine?

 

[dcackers]

Hello,

Thankyou for your reply.....yes the heating works absolutely fine!

Daniel

 

[kitch0978]

If you can look underneath boiler when you have hot tap open can you see the dhw diaphragm spindle sticking out and pushing the microswitch?

 

[dcackers]

Hello,

Sorry i really wouldnt know where to start looking.

Could you describe exactly where I need to look?

Thanks,

Daniel

 

[Homesafe]

Plumber might be right ,on this one

 

[dcackers]

Hi,

Sorry, have managed to suss out the diaphragm spindle location....

Yes it pushes the microswitch when the hot water tap is opened. Plus the potentiometer (dimmer light switch style knob) adjusts the temperature of the water correctly.

All help is much appreciated!

Daniel

 

[Homesafe]

What do you think kitch, H ex ?

 

[dcackers]

Any suggestions anoyone?

 

[dcackers]

Nobody???

 

[Homesafe]

Blockage or scale in hex or pumpp knacked.

 

[Agile]

I think you need a competent engineer and not a parts changer which you seem to have.

I hope he is not charging to change parts which dont solve the problem.

A fault which presents all the time is easy to diagnose. The only problem is ones which are intermittent.

I have to deal with a tenanted property where only one of four tenants gets an intermittent fault. Thats very odd !

Tony

 

[kitch0978]

ok, could be the water heat exchanger or possibly the burner pressure is too high and with a slightly blocked heat ex it is struggling to get rid of heat quickly enough, you need to get a decent boiler engineer in to find out wat problem is, someone on this forum may be near to you.......

 

[richw]

I had the same problem with mine.

First thing you should try is to change the CH thermistor. I know it sounds strange, since your problem is with the HW, but the design if the boiler means that in HW mode, both thermistors are important. The CH and HW thermistors are the same, so just put your spare one in the CH side.

If you monitor the voltage at the DHW thermistor, you should see it change as the HW heats up. In response to that, the PCB should tell the gas valve to reduce the gas pressure (modulating). Use a multimeter to check the HW thermistor is working, and the signal is getting to the PCB. Then check the PCB is trying to adjust the gas valve by measuring the voltage across the purple wires.

It could be that the modulator on the gas valve has failed, so it always runs on 'full' with HW. This will cause an overheat in the internal CH loop, which will shut off the flame. Does the flame alter in size when on CH? (the CH uses some modulation)

With mine, as stupid as it sounds, there was a break in the wires joining the HW potentiometer to the PCB. So in HW mode, it was always on full gas, which would overheat. Once the wiring loom was replaced, the HW sensor was able to notify the PCB, which was able to modulate the gas valve. So no more cutting out!

There is quite a lot you can do if you use a multimeter and common sense. The fault finding chart in the manual is a bit of a red herring, I think!

If you can, check the min and max gas pressure settings on the gas valve. This is quite easy to do if you have a manometer - otherwise leave it for an RGI.