Boiler over heating

[RickWard]

Hi,

Have just moved into a new commercial unit. Unit was fitted with a Potterton Profile 100E boiler running central heating for 9 rads - all previously working as far as I'm aware.
Had the boiler and a few rads relocated last week but now cannot get the boiler to run without the over temp stat tripping.
Originally assumed it was air in the system - spent a long time purging the system but made no difference.
Thought the rads maybe clogged or pump was weak. Replaced the pump and took rads off and flushed them out but made no difference.
Checked the over temp stat with a kettle - tripped around 100C
Saw there was 2 other thermostats fitted - boiler stat on return pipe to boiler and water temperature stat fitted to rear of boiler on the return side.
Boiler stat switches and appears to switch at different settings when the pipes get warm.
Not sure of the function of the water temperature stat - seems to operate the pump ? Does this stat regulate the boiler if there is no flow i.e all rads off ? Could this be faulty ?
Assuming stats are ok - guess water flow is the issue ?
Idea's ??

 

[alan m 1974]

Is it doing hot water as well,I would make sure your fully pumped or gravity switch hasnt been knocked over by accident

 

[RickWard]

No - boiler is for central heating only.
Switch is set to fully pumped

 

[bengasman]

got to be a flow problem somehow. did it work at all since the work?

 

[RickWard]

No - always tripped on the over temp stat since work started
More or less convinced myself that there is an issue with flow
Was thinking of running a bypass between the flow and return with a gate valve to adjsut the flow - sound sensible ?

How does the boiler cope with a system with TRV's on every rad i.e if all are closed hence no flow what stat would turn off the boiler ?
Is the water temperature stat the guilty part ? Pretty sure I can hear a stat clicking minutes before the over temperature stat trips .

 

[Gasguru]

You must not have TRV's on all the rads, otherwise when the rooms are up to temp there will be no flow. It is also likely to contravene building regulations and waste energy. A room thermostat should be fitted with an uncontrolled radiator. Read the manual - it gives the minimum flow requirements.

What do you mean by "Saw there was 2 other thermostats fitted - boiler stat on return pipe to boiler and water temperature stat fitted to rear of boiler on the return side." The boiler themostats are inserted into dry pockets in the heat exchanger.

 

[bengasman]

Rads in room with roomstat must NOT have trv. You must have a bypass, but NOT to sort this problem out. Auto bypass now compulsory, not the old gatevalve trick

 

[RickWard]

Agreed - room stat = no trvs.
Just interested to know if all rads on trvs and are closed what is the controlling stat to turn the boiler off before over temperature trips.

Can see 3 thermostats in boiler - read inserted in pockets
Over temp stat - flow side heat exchanger
Water temperature stat - return side heat exchanger
Boiler stat - return pipe

Bypass would be to prove a point to see if flow was the issue.

 

[bengasman]

Just interested to know if all rads on trvs and are closed what is the controlling stat to turn the boiler off before over temperature trips.

roomstat