Potterton suprima 60 boiler fault

[wickywise]

I have a Potterton Suprima 30L-100L boiler which has had the PCB upgraded.
I had a problem with hot water venting into the header tank and called a plumber who changed the pump. It still vented until he turned the pump to the lowest of it's three settings. This then resulted in the radiators getting barely warm. Under a maintenance contract another plumber called to check the boiler and determined the Thermistor needed replacing because the boiler was not producing enough hot water. That did not work and a blockage in the central heating was suspected.
I am now three days into flushing the system with Fernox.
My question is: would a blocked system govern the firing time of the boiler? At the moment the boiler only fires up for 30 seconds every two minutes? This appears to be too little to heat the system and the supply pipe above the boiler gets hot but not as hot as one would expect.
Any advice would be greatly appreciated.

 

[nysk2008]

What is the heat like in your rads? Any cool patches etc? It would also be worth checking the flow and rtn tems. what happens when the pump is turned to 2 or 3? is this a recent issue or have you recently moved to the property?

 

[wickywise]

Thank you nysk2008 for your return. About two months ago I noticed really hot water venting into the header tank and as I said the pump was changed and the venting only stopped when the pump was on the lowest speed. Since then the rads only get warm for the majority of the time but very occasionally they do get hot but only for a short time. I have checked the flow and return pipes above the boiler and the flow gets hot after a thirty second fire-up and the return is hardly warm. I currently have the pump on the highest of the three settings but there is no venting due to the low temperature of the central heating water. I feel that the boiler is not running for sufficient time to heat the water properly and wandered if a blocked pipework would cause the boiler to turn off prematurely. I have been flushing the system for four days now but nothing appears to have changed. Hope this helps.

 

[AWheating]

one thing to try

run a magnet over the pipework in your air cupboard, especially the feed and vent pipework and connections. If the magnet sticks its probably full of sludge.

 

[wickywise]

Thank you for that AWheating. I have already tried that with the only magnet I have which is one of those novelties you stick on the fridge door. I will get a proper magnet and try again. I concentrated on the area around the Airjet as this is where the return flow joins the venting pipe, the feed from the header tank and the return flow through the pump. It seems if there is a block this is the most likely place.

 

[nysk2008]

is the boiler locking out and a manual reset is required? TBH it sounds like a circulation issue. Although dosing the system with something like senital x800 or fernox can work it may be worth looking at the powerflush option - if you are competent the machines can be hired for about 50 quid a day + the cost of chemicals - something like kamco FX2 would be good. If you can, remove the pump and flush from there as sometimes if done from a rad the results arnt as good. Also as AW Heating has suggested check your feed and vent and these do and can become blocked - I would check that first before the flush.

 

[wickywise]

Thanks for that nysk2008. Apart from HSS, who quote from £89 per day, all the other local hire places are closed. However, it is an option I didn't know about and if my current flush does not work I will give it a go. Thanks again.