BM II Issue - Need help diagnosing HW fault

Hi there,

I have a BM II which is still heating perfectly but is offering up occasionally hot (for 60 secs or so) and mostly luke warm water.  I have done a lot of reading online and am still struggling to identify my issue.

Situation is as follows:

• It was working perfectly up until 24hrs ago so although we live in a hard water area I would have assumed that if it was scale it would have failed gradually.
  

• The top up tank is filled up to the correct level
  

• The thermostat control seems to be working, on the occasions when there seems to be some warm water in there it will 'click' turning the green light on and off
  

• I have taken both screws out of the pumps and they are both spinning OK
  

• The mixer valve feels warm to touch until I turn on the hot tap at which point it turns cold
  

• Usually when you turn on the hot water the boiler will fire up with 60 secs or so. Since we have had issues it does not do this

From what I have read the most likely problem is:

Thermostat - If this had failed would it make the water in the heating cooler as well?
Water no getting into the tank - Is there anyway I can test this?
Mixer valve - Again is there anyway I can test this?

Any advise would be much appreciated!

Water not getting into the tank - OK, I have checked this, emptied some water out of the system and it refilled (albeit slowly).

I am going to order a new mixer valve and give that a go.  

Thing that is confusing me is the exterior skin of the store feels cooler than usual leading me to think it is a thermostat/ heating issue.  Hopefully I am wrong and it is the valve!

From my limited experience of these units, you can interrogate both the boiler and the boiler mate II.
You can see what temperature each sensor is showing.
Think there are 2 or 3.

Top, Middle or Bottom.

If heating working would suggest thermal store ok.

The tank on top is the overflow tank (I think) but will have some liquid in.

There should be a fill loop for the radiators (Red metal cylinder)

But this just adds water to the radiators (may also interact with water in the store)

Ours is set to 1.5 bar when system hot.

We had a problem where position Y valve stuck and the radiators got hot.
This was in the middle of Summer with the heating off.

There will be a zonal valve that should shunt automatically.

I would say this is the culprit.

There is another valve on the pipes too.

One of them interacts with it I am sure.

Strange that the boiler does not detect the water has been run.

On ours even a dripping tap causes the boilermate to start whirring away

You could try use the immersion heater feature to see if you get hot water too

If the unit is hot.
You can put your fingers inside where the boiler flow enters the unit and feel the tank.
If hot then it should work.

But how you have described things it does sound like the mixer / blending valve has failed.

Mike

mike wrote:If the unit is hot.
You can put your fingers inside where the boiler flow enters the unit and feel the tank.
If hot then it should work.

But how you have described things it does sound like the mixer / blending valve has failed.

Mike

Hi Mike,

Spot on, I removed the mixer/ blending valve and it had failed, all the internals fell out as I removed it.

Replaced it a couple of weeks ago and it has been perfect since.

I found this site really useful when trying to pin down what the issue was so thanks for a great resource.

Thanks to Hawkeye for your input as well.

Cheers,  Matthew