Boilermate III - Hot water problems

[zannazak]

Hi,
Looking for some help to diagnose a problem with our boilermate III. Ten days ago, we suddenly started getting problems with our hot water. You would get an initial burst of hot water for about 20 seconds, and then it would go cold and not heat up. The central heating is fine, and is unaffected.

We called out an engineer, and they said it was the blender, which they replaced. This made absolutly no difference. So they said they thought it was heat exchanger and have just replaced that, but the problem has not gone away. Although it is slightly different. You can now run the hot water tap at a low flow rate and it will maintain hot water, but as soon as you put a normal flow rate through it goes cold again. We've checked the PCB and there are no errors, and you see the DHW temp plummet from mid 50's down to 20's when the tap is turned on. Don't think it is the sensor as you can hear the pump turn on. This just doesn't seem to make any difference.
The latest idea from the engineer is that it is sludge causing the problem. Do you think this likely? They are talking about flushing out the system, which I know is expensive.
Any advice you can give would be greatly received.

Thanks,
Rosie

 

[twgas]

do the pipes either side of the pump stay hot as the water is drawn off

 

[superdupergasman]

Are they sure that the boilermate is properly filled up with water,
famous for the cold feed blocking up and not filling properly, pump may be pumping air and water hence a bits of hot water cleared with a bit stiff wire.

Alternatley I am sure there are 3 sensors one for store temp, one for DHW temp and 3rd for flow from boiler temp...could be latter thats faulty....although I may be gettting confused with the 2000 model.

What temp is the boiler set to....should be up to max to heat store properly....how is the heating working??

 

[zannazak]

Thanks for the replies so far.

The pipes either side of the pump start off warm, but as the hot tap is turned on both sides go cold and don't warm up again. What does this suggest?

The central heating is fine, and we've checked that the top storage tank on top of the Boilermate is filled up to the embossed line.

The boiler itself is set to its maximum temperature.

Cheers
Rosie

 

[superdupergasman]

The header tank will look full but if the pipe going from this into the store itself is blocked then it wont fill.

The next question is the boiler set for hotwater 24/7 and is it reaching the 82oC on the flow to the store?? ie is the store up to operating temp when HW is called for.....if the store is not hot enough then the hot water will be poor.

 

[zannazak]

Hmm... there is some gunk in the header tank. What's the best way to clean out the pipe connecting it to the store?

The store temp low/high values are 72/76 and it usual sits fairly happily in between those. Is that too low? If so, how do I go about adjusting those settings?

Thanks again.

 

[superdupergasman]

A bit of stiff wire to feed down the pipe, easy way to test the tought of a blocked cold feed is open the drain to the CH system, then see if the header starts to fill up.

That would prove its clear or not.

So we are confident that the store is up to temp and its full of water,
what about the pump to the DHW heat exchanger?? it may feel like its spinning but the impeller could be sheared off it.

 

[Phil11]

I have known sensors to be faulty even when no errors show on pcb

 

[zannazak]

Thanks for the advice,

We have attempted drain some water from the cylinder and the header tank doesn't seem to be filling up, so we can tried to clean out the pipe, but there doesn't seem to be a blockage.

We drained about 5-6 litres of water and towards the end it started to make a gurgling sound. Could we have air in the system? If so, is there anyway to clear the air?

Cheers,
Rosie

 

[superdupergasman]

did the wire go all the way into the bottom of the store as that tube is quite long.

you could keep draining and hope the air lock clears??

 

[nickso]

backfill it if the cf is blocked.

if the dhw circuit is airlocked i run a tap and undo the exchanger nuts to release the air, works 50% of the time. sometimes they wont clear for love nor money. be careful undoing the exchanger nuts as it may leak afterwards and it goes without saying dont take them completely off