Potterton Profile 100e Pump continuously on, odd firing

[landbeach]

Well as it's the last thing I can realistically disconnect, thought I may as well give it a try.....but surprise surprise - pump running, boiler fires!

 

[tonybhoy]

Your gonna have to bite the bullet and get in an electrician.

Make sure they know about heating systems but my money is still on the stat/MV.

Best of luck.

P.s I'm surprised D_Hailsham hasn't been on this thread. He's pretty spot on with stuff like this.

 

[Timd01]

I think either the pump o/run stat is U/S or if its since the fans been replaced, it is the fully pumped/gravity switch in the wrong position!
READ the M.I. and make sure this switch is in the correct position for your system.

 

[namsag]

Tonyboy how can it be the roomstat ,the roomstat gets its power from the switched side of programmer .With the programmer in off position if there was power going to room stat it would mean faulty programmer.
But the programmer has been completly removed so there should be no power at all going to the roomstat at all to activate anything.

There is a permenant live getting to the boiler somehow on the switched live side.
Not by any chance someone has linked both at the boiler.

Faulty pump over run stat /or switch in gravity position would not give a live to the gas valve side

 

[Timd01]

If the o/run stat is shorted on N/O and the gravity/pumped switch is on gravity this will give a P/L to the S/L on the board.

That is why I would be checking both.

 

[tonybhoy]

Tonyboy how can it be the roomstat ,the roomstat gets its power from the switched side of programmer .With the programmer in off position if there was power going to room stat it would mean faulty programmer.
But the programmer has been completly removed so there should be no power at all going to the roomstat at all to activate anything.

There is a permenant live getting to the boiler somehow on the switched live side.
Not by any chance someone has linked both at the boiler.

Faulty pump over run stat /or switch in gravity position would not give a live to the gas valve side

Just going on a recent experience with a Glowworm Ultimate( I think) I had which was exactly the same as this one and turned out to be the roomstat after having replaced both MVs.

In that case I removed the programmer face plate and the boiler still fired.

I did tell the customer the MVs didn't require replacing however they were old and cr@p ones which I replaced with Honeywell ones ,customer was happy.

 

[landbeach]

Heating engineer visited this evening - and sorted the problem!!

Both motorised valves had +240v at both the orange and grey wires!
Frost thermostat was not firing boiler when activated.
Engineer got some weird voltage differences across terminals in the boiler.

Then he noticed that there was a short bridging wire connecting the permanent live and switched live in the boiler. He had already checked the connections on the 'installation' side of the boiler's connections - but the bridging wire was across the pre-wired side of the terminal block.

With this wire removed, whole system performs correctly and voltages across terminals returned to correct values. Engineer said he could think of absolutely no reason why somebody would have done this!

Chuffed with the engineer for resolving the problem - definitely a tradesman that inspired confidence and excellent value too (only a £10 charge on top of the £50 service)!

Thanks to all on here for the suggestions!

 

[cider]

id bet whoever wired it first time round didnt put enough wires in for pump live switch live etc so just looped the lot together in boiler to stop overheat stat tripping