Extremely hot water

I have a system comprising of a Glowworm Micron 40FF boiler and a Boilermate 2000. My problem is with the temperature of the DHW which to me feels as if it is pretty much at a scalding temperature. When I turn on a hot tap, the water initially warms up to a comfortable temperature it then cools down slightly before then increasing to about 65-70 degrees, which I have measured with a temperature probe. Having looked inside the Boilermate and going through the ACB read out, the store temperature reads around 73-77, the PHE sensor was fluctuating between around 40 and 85, and the DHW sensor was reading between about 59 and 65. I discovered that a reading of 85 can indicate the PHE sensor was faulty, particularly as the readout varied when wiggling the wire proximal to the sensor and I have since replaced that. It now gives a reliable reading in the 30-45 degree range. I have also examined and bled the 3 Grundfos pumps and ensured that they are all turning freely. A new problem started a couple of weeks ago, where there seems to an issue with the overrun on the Boilermate circulation pump, which I understand should be for 3 minutes after the boiler shuts off. The pump runs pretty much continually for hours on end, until either I turn the Boilermate off and on or I turn on a hot tap. My hunch is that this whole issue is related to the ACB. There doesn't appear to be a fault with it as the readouts would appear to be correct, but I imagine there is probably some underlying issue with a component. Unfortunately replacing the PHE sensor didn't seem to change anything! I would be grateful if anyone had any thoughts/advice, as I don't want to be coughing up the 230ish quid for an ACB, only to find that it didn't cure the problem!

Depending on age.
It can be wise to change sensors.
But it does sound like the ACB.
Try switching the unit off, waiting then back on.
This re boot sometimes.
Mike
MGC/H2O

Many thanks Mike for your reply.... The system is about 6 years old. As I said I have replaced the PHE sensor, but am wondering now whether it would be an idea to replace the other sensors too.... As I understand the store sensor is pretty reliable, but wonder whether I should replace the DHW sensor? What would the symptoms of a faulty DHW sensor be? It's reading doesn't seem to fluctuate at all when wiggling the lead but am not sure it is 100% reliable...
When the circulation pump is overrunning if I turn the unit off and then on again it does seem to sort itself out only to repeat the next time the unit calls for heat. I am thinking that the next step might have to be replacing the ACB. Having examined the board, there is some discolouration around the relay contacts, so it is highly likely it will need to be replaced... Just want to make sure that if I fit a new ACB there isn't some underlying problem which will cause it to happen again!

I would change the DHW sensors next,
Mike
MGC/H2O

Thanks Mike, yes I think I will replace the DHW sensor next, as it is easy and relatively cheap to do.

Right I have now replaced the DHW sensor and decided to go the whole way and also replace the ACB to try and sort this out! Fortunately this seems to have sorted out my scalding water problems. The only issue I have now is the store never seems to reach the T1 off temperature. When the temperature drops below T1 on, the boiler comes on as it should and continues heating until the store is around mid way between T1 on (70) and T1 off (77) at 74 degrees when it then shuts off. As the store temperature hasn't reached T1 off it continues to call for heat though and boiler pump keeps running. But the boiler doesn't come on again until the store temperature drops down again to T1 on.

Could air in the system cause this problem, as I reckon I could well have introduced air in to the system when I drained and replaced the PHE sensor as I imagine that air in the heat exchanger would cause a drop in heating performance. I can't see an obvious way of bleeding air out of the system, but then I am not a heating engineer! I think the boiler should be fine as it was serviced recently and passed with flying colours, but wouldn't exclude it!

Many thanks
Julian

If air is trapped you can loosen a nut on the PHE (top)
Did you programme the ACB ? To your unit?
Mike
MGC/H2O
Norfolk

Hi Julian
I also had very similar faults which I only managed to resolve with the replacement of the main board (expensive I know).
Strangely enough this happened after I also had to change the temperature sensors.I was suspicious that by turning the BM2000 off and on several times to complete this work, I may have somehow induced a 'spike' from the small arc in the switch, which may have contributed to the demise of the electronic board.
I decided after replacing the board, to plug the BM2000 supply through a computer protection plug/socket. This uses capacitors to smoooth out the sharp electronic spike which can cause such damage to electronic boards.
A small point but for the cost of this investment it may save the cost of another main board.

I am not sure if this helps you too much, but in the case of the board replacement may be worth it.

Kind Regards

Richard

Yes I agree with what Richard says.
And I always wear gloves when fitting any PCB.
I have some similar to aircraft fitters use.
The BM 2000 is very delicate with regards to;
Spikes
Surges
Lightening (in the area)
And handling too.
The ACB has a fuse fitted but it might as well be a metal bolt.
As in most cases if the fuse goes for what ever reason, it is just luck if the ACB stays intact!
I have been looking into surge protection too.
Some BM 2000's have the "switch back up" so care must be taken.
Mike
MGC/H2O
Norfolk