Potterton System Boiler with no hot water

[BintyandtheBeast]

Hi everyone,
Hoping for some help please.
We have a Potterton Performa System 24 HE with Megaflo tank which has stopped heating water. House built in 2009 and central heating system is therefore 8.5 years old.
The programmer has been replaced and is on constant calling for hot water.
We have 2x Honeywell diverter valves next to the Megaflo tank which have been replaced despite apparently working correctly as they were original. I can manually open the hot water valve when the boiler is running for heating and it flows through fine on to the cylinder.
If I run the electric immersion then I get hot water from the sylinder
I've also this morning replaced the PCB and it's made no change.
Any help for what else may be the issue?

 

[picasso]

Stop throwing parts at the problem for a start, if you have a multimeter check the tank stat is ok.

 

[BintyandtheBeast]

Hi picasso, just tested the stat with a tank of cold water and power is not flowing, it's just closed.
Thanks for your input, I'd assumed that that because there's a stat on the PCB there wouldn't be an additional on the tank - bad assumption. I guess that's why I'm not a heating engineer!

 

[BintyandtheBeast]

Ok, now I'm doubting myself!
I get a reading close to 0 when connecting my multimeter to the top left and top centre connections, and 1 when I connect top left to top right. Cylinder is cold.
So does this confirm its the tank stat?

 

[picasso]

With the power off you should have continuity between 1 and 2 on the plastic strip connector, with the power on there should be 230vac on both 1 and 2 if the stat is ok, test between 1 and 2 to earth.

 

[BintyandtheBeast]

Thanks again picasso, I appreciate your input.
Turns out that one of he terminals wasn't screwed down!! After 8.5 years of no problems it decided to stop. Screwing it down and putting it back together seems to have done the trick!
Fingers crossed that's it sorted long term.
Thanks again.

 

[heatservice]

Expensive DIY repair then, 1 x programmer, 2 x zone valves & 1 x PCB, stick to your day job as a little knowledge can be expensive as well as dangerous.

 

[BintyandtheBeast]

I was lucky to only need to buy one of the valves and a refurbished PCB. The other valve was left in our attic along with a programmer and a load of solder fittings and a coil of Hepworth pipe when our house was built, presumably by the same plumber who didn't tighten the cable connection at the cylinder. We've actually had the PCB changed twice due to failure: once after a year and the other in 2013 with new boards. I bought a refurbished unit from someone my local plumb centre manager recommended, so not as expensive as it could have been, plus I now have a spare board if required which I know is good.
Zone valve was £30 on eBay delivered too and maybe a good preventative measure.
I'll get back to my day job for a while, and thank you again for your help picasso.