Not enough hot water - Potterton Suprima 30?

Hi All,

We have had the above boiler and Boilermate II for the last 8 years and have had no problems with either central heating or hot water.

2 weeks ago however, the hot water turned cold after only a minute or so in the shower and it has been so ever since. We have hot water initially on all taps and turns cold after a very short time.

We checked the central heating and it seems to be working properly. We have not changed any settings etc. The red light (power) in the bolier is on and does not require re-setting (though we did that too). The bolier is firing up in its usual intervals and goes on in the same way as before, but we simply don't have enough hot water, it used to last forever or we never run out.

Very puzzled, can anyone help please?