Water-to-Water Heat Exchanger removed from boiler. This was removed by undoing the main nut connecting it to the diverter valve in addition to removing the jubilee clip and screw from the return flow manifold. The other two ports connect to the boiler merely by sliding in to female unions relying on the o-rings to provide a seal. You can see in the middle port (DHW inlet) that there is a flow limiter to reduce the hot water flow - remove this and clean as this may well have debris in it. For all ports, new o-rings/washers are required as necessary.