Potterton Lynx 2 boiler not starting up!

[bjandthebeans]

Hi

I recently experienced a non-startup fault with my Lynx 2 boiler following a power cut last Tuesday. The power was restored during it's active evening period and the boiler operated normally. However, it never activated again the following day. It has been a good, reliable boiler down the years and I followed the normal repair procedure set out in my handbook. The fault, on 'switch on', is no DHW being heated, no LED lights illuminated on the control panel - nowt! When the CH facility is switched on - nowt except the pump kicks in albeit a noisy operation. On test, 230v ac 50Hz measured at the PCB terminals and the 24V ac transformer is good - 3 x windings tested for continuity and sound. I decided to swap the PCB for a spare one (as mentioned in the handbook repair assessment) but same symptoms persist. Tried another PCB - same again! I'm stumped! It appears that something is externally restricting the full operation of the control board but I'm unsure of the cause. Could it be a blocked or malfunctioning pump? Has any other user experienced fault symptoms like this one.? Any useful comments appreciated.

 

[Millsy 82]

Over heat stat has probably popped I cant remember where they are on that boiler look around for the little red button the middle bit will probably be sticking out

 

[bjandthebeans]

Thanks for the prompt comment but note there are two overheat stats (A DHW stat and a CH stat) fitted to this Lynx 2 boiler - they are solid state stats with a double screw connection and a flat heat conducting pad (dia about 1 cm). They're not fitted with a reset button, as described but I'll test the OH DHW stat for an open circuit and replace - hopefully I'll get lucky on this conundrum! If not, then momentarily short cct the CH flow switch and see if the boiler starts up?

 

[Millsy 82]

Do you have continuity on them, Failing that there is a water pressure sensor might be blocked up or faulty

 

[bjandthebeans]

There is a water pressure diaphragm switch fitted to this boiler but my boiler pressure reading has been a normal steady reading of 0.5 bar for long enough so I'm less inclined to suspect this sensor. Also this part was fitted as a replacement a while ago and is still fairly new. The stats and water flow look like good suspects - worth mentioning the pump is noisy and laboured but is rotating (could be a source of poor water flow, old pump and 20 years old)! I'll check them out tomorrow.

 

[bjandthebeans]

Both OH thermostats are reading OK so no joy on that front. I'm beginning to suspect the water pump or flow sensor - never seen the effect of a blockage or flow restriction but I'm assuming the control pcb operation would be shut down if the flow sensor activated.

 

[Millsy 82]

Disconnect the flow sensor lead from board turn boiler on do you have continuity after that start working through ignition sequence

 

[bjandthebeans]

Thanks again. I'll do this tomorrow and check if the flow sensor activates on a short or open circuit and take it from there. I hope it is the culprit as, after that, the sequential test becomes tedious but the only way to progress to a remedy!

 

[bjandthebeans]

I tested the flow sensor and no reading when the pump kicks in. Shorted the switch contacts and, hey presto, I triggered the ignition/heating sequence. Boiler heated up on 24hr CH activation. Switched off CH facility and turned on a DHW tap - got hot water. However, after refitting the electronic panel cover plate, went to test CH again - back to same fault, water pump only activating. DHW not heating any more! No ignition sequence. Tried a full short cct on the flow sensor terminals - no response this time.
Drained the boiler and whipped off the flow sensor - readings OK and paddle moving freely; so tested OK. I replaced the water pump - still no flow indicated on the sensor. I'm beginning to suspect my motorised valve but this is an expensive item. I wouldn't mind a second opinion and also why did my control board not respond again after my initial successful test? Has another protective switch kicked in?

 

[Millsy 82]

If it worked when it was shorted out then you have proved it was a circulation problem. If you left the short on it when there is no pump on it may register as a fault within the boiler. Cant see it being the 3 port valve in the boiler as the water has to go past flow sensor if it was stuck centrally then there would still be a flow going past as the returns join together inside the boiler. If the flow switch is opening and closing as it should then it is either a blockage in the boiler or where you have shorted out the board you have caused damage to the board.

 

[Millsy 82]

Also is the pump on the correct way round should be pumping up towards the heat ex

 

[bjandthebeans]

I've got two other good boards but no chance of me fitting either until my flow switch tells me I've got water moving in the boiler system again. Likewise, I certainly suspect a blockage but unsure where - maybe flushing out the system might get a result. When I drained the system today, I did notice there was a fair amount of rust gunge at the tail end of the drain period and the CH expansion tank was not so keen to drain out in the way that it normally does, from start to finish, although it did eventually start pushing out the water until empty. I'll target the pipe entry up to the CH expansion tank - defo the chief suspect in blockage terms (might be be at the entry point to the tank!).

 

[bjandthebeans]

Aye. It's a Wilo pump and I made sure the flow direction is as before. I've got two other good electronic boards but no chance of me fitting either until my flow switch tells me I've got water moving in the boiler system again. Likewise, I certainly suspect a blockage but unsure where - maybe flushing out the system might get a result. When I drained the system today, I did notice there was a fair amount of rust gunge at the tail end of the drain period and the CH expansion tank was not so keen to drain out in the way that it normally does, from start to finish, although it did eventually start pushing out the water until empty. Also when the pump is active, it sounds like the water isn't moving freely through the exp tank. I'll target the narrower pipe entry up to the CH expansion tank - defo the chief suspect in blockage terms (might be be at the entry point to the tank!).

 

[Millsy 82]

It wont be the pipe to the expansion vessell as that only comes of the pipe the best bet would probably be get somebody who deals with breakdowns alot to come out chances are its something little and silly that will only take them half hour to find and resolve. I used to work alot on these boilers and they are fairly straight forward but its probably been 8-9 years and I cant remember a huge amount.

A check to do on your expansion vessel is let the air out if the pressure drops theres no blockage. But remember you have to top up the air.

 

[bjandthebeans]

Thanks. I'll do that last check on the expansion tank after I flush out again - previously done it using a portable tyre pump. I agree it's almost time to bring in a competent HE to suss this out if unsolved.

 

[ecowarm]

:42: :42: :42:
Spam, spam, spam

 

[bjandthebeans]

Before getting stuck into the CH Expansion vessel, I decided to up the water pressure in the boiler and, hey presto, the water pressure switch was giving duff readings! Got a spare one in my plumbing box, drained the system again and, Houston we have ignition! :smile: All tests OK and I'm glad I fitted the new pump that I've kept spare for a while - a sweet sounding piece of kit compared with my original noisy one! Phew, another crisis over :teeth_smile: