sludged pump?

Bungalow:
Grundfos hot water circulation pump failure. Kitchen around 20mt from storage tank so the pump failure means hot water takes along time to get to kitchen. All other taps to sinks,bath, showers in area of storage tank work fine, its just the kitchen thats slow. British gas cover 200 covers this pump but they have refused to replace it due to sludge being cause of failure. How, I asked, can the engineer say it's sludge. 'He has equipment to test for sludge without removing the pump.' I discused the pump with the engineer and he never said anything about sludge. Are they using this as a get out as i've never heard of sludge in a hot water system, lime maybe but not sludge.

I don't think its either as the pump stopped so suddenly. Are they pulling it or not? they have change the central heating pump I suppose they consider that enough expense for this year.