Low Domestic Water Pressure fromy my Valliant ECOmax 824E?

I'm experiencing low water pressure at the hot tap. I have a Valliant ECOmax 824E combi-boiler. I've had this problem before, coupled w/no hot water, and I replaced the heat exchanger. This worked, but I've done this 3 times in the last 1 1/2 years. This time I have hot, but no pressure. I took the heat exchanger off, and descaled it, but it didn't work. Pressure gauge reads in normal range, and heat works good. Can anyone help?