[BrendanP]

The heater on my old FD 1.6 diesel has not been very effective lately, so I want to try reverse-flushing the heater matrix to restore flow. When the engine is hot and running, one of pipes going through the firewall is hot, the other is lukewarm. Am I right in thinking the hotter pipe is the flow to the heater, and the cooler pipe is the return? If I flush it I should feed the fresh water into the return pipe. Standing in front of the car, the hotter pipe is on the left and the cooler pipe is to the right of it. Can anyone tell me the diameter of the pipes so I can get some flexible tube the right size to fit over them?

[PGN I30]

I've only ever flushed one on a BMW Mini, it didn't help much and eventually it was replaced, you can try a descaling solution if it's scaled up but you may risk a hole developing if it's badly scaled.
Can you not remove the hoses and reverse flush with a hose?

[BrendanP]

That's what I was planning to do, reverse flush it with a hose pipe. I was just wondering what diameter the pipes are. I found a drawing of a pattern part that shows them as 19mm. B&Q does some clear plastic tubing that is 19mm diameter so I'm hoping it's stretchy enough to fit over the heater pipes