Ideal Isar boiler problem

[Chappers]

Hi,

I've got a problem with an Ideal Isar condensing combi boiler. I can't see exact model number of it anywhere though, I'm afraid. It'd be a big help if anyone can please offer some assistance.

It's been working fine for years and was not touched before the problem started. DHW and CH temperature control knobs both set to maximum and been that way years too.

Today it started purging water out of the overflow pipe, and a quick inspection showed the CH pressure so high it was beyond the 4 Bar marking on the scale. The boiler was still running and showing no fault codes.

I used the drain valve to reduce the pressure back to 1.5 Bar and ensured the filling loop wasn't partially on or letting by when off. Started the boiler up again and watched as over the space of minutes the pressure steadily climbed to around 4 Bar and started purging fluid again. It carried on running with no lockout or fault codes, just the noise of the relief valve operating.

What I've done for now is turn the temperature control knob for CH down to midway position and the boiler is running happily with the CH pressure oscillating between just under and just over 2 Bar, with the needle flicking a bit the whole time the boiler's running.

What's likely to be the trouble? I assumed overheating of water in heat exchanger causing pressure rise, probably due to failing pump. However, if that's the case, why aren't the control thermistors or overheat stat causing the boiler to enter lockout? Are there other causes of this behaviour?

Thanks for any advice.

 

[the baker]

Was the system cold on your arrival or was it hot?

If it was already hot it may be the that you need to check the pressure in the expansion vessel?

If there is bu*ger all air in the expansion vessel the system water has no where to expand into so makes a sharp exit via the OPV.

If you are able, isolate the boiler at the isolating valves, drain off the pressure from the boiler, and check the Expansion vessel pressure at the schrader valve, the valve is acessible by taking off the White case, and removing the galvanised panel that encloses the fan/combustion chamber etc.

The valve can be seen behind the fan, its central.

If the Expansion vessel is knacked and wont re-presureise it looks as though its a boiler off the wall job, unless you can fit a Robo kit some where else on the system.

Tim

 

[Chappers]

Thanks a lot for the help. The pressure was like that when hot. After being turned off and cooling, the pressure returned to its normal level. Putting the boiler back on causes the presure to rise excessively again within 5 to 10 mins.

I'll have to check the expansion vessel and go from there. Thanks again.