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[pscocoa]

Do you have thermostatic valves on most or all the rads?

yes

[PhilRich]

Do you have thermostatic valves on most or all the rads?

yes

If there isn't a dedicated by-pass fitted to the system then one rad needs to be fitted with manual valves at both ends or else the system wont have a constant circulation in the event all thermostatic valves are shut at any given time.

[pscocoa]

Do you have thermostatic valves on most or all the rads?

yes

If there isn't a dedicated by-pass fitted to the system then one rad needs to be fitted with manual valves at both ends or else the system wont have a constant circulation in the event all thermostatic valves are shut at any given time.

Thanks - just checked 5 out of 12 are thermostatic so gave wrong info in my previous post -

[Andy H]

I had a Potterton Prima in my last house (previous model to the Suprima, I only had to change the PCB once  )

The recurring problem I had was that the microswitches in the 3 port valve would burn out because they were not suitable for carrying all the current required by the boiler and pump.

[PhilRich]

I am assuming this is a conventional indirect heating system with boiler, hot water storage cylinder & feed & storage tanks in the loft/above the cylinder? If so, check that the ballvalve supplying the heating system (smaller of 2 tanks) hasn't become jammed shut & the tank still has water in it? :-/

[pscocoa]

I am assuming this is a conventional indirect heating system with boiler, hot water storage cylinder & feed & storage tanks in the loft/above the cylinder? If so, check that the ballvalve supplying the heating system (smaller of 2 tanks) hasn't become jammed shut & the tank still has water in it? :-/

yes -system is as you describe but it is working fine right now and since about 5pm.

Point tp consider also is in MDTMs post re. internal trip - question would the internal trip generate a lock out /red light or just cause the boiler to hang in burner off mode?

[PhilRich]

I am assuming this is a conventional indirect heating system with boiler, hot water storage cylinder & feed & storage tanks in the loft/above the cylinder? If so, check that the ballvalve supplying the heating system (smaller of 2 tanks) hasn't become jammed shut & the tank still has water in it? :-/

yes -system is as you describe but it is working fine right now and since about 5pm.

Point tp consider also is in MDTMs post re. internal trip - question would the internal trip generate a lock out /red light or just cause the boiler to hang in burner off mode?

If it's working correctly it should cause a lock out

[Kevin Wood]

I had an issue with one of my motorised valves that the valve would occasionally close when the thermostat is satisfied, but the microswitch would jam closed, meaning that the boiler is working into the bypass circuit (which, in my case, includes 2 bathroom radiators, so the boiler didn't get unduly upset).

If there is little or no heat load on the boiler in this state I could imagine it might lockout. Waggle the thermostat and the microswitch might unstick.

Failing that is the pump starting reliably? Could be that the capacitor is failing (it's in a pretty hostile environment) and the motor isn't starting reliably.

If the boiler starts OK the only thing on the PCB that might be suspect is the relay that controls the pump perhaps? Certainly not worth changing without further diagnosis IMHO.

Kevin

[pscocoa]

new pcb fitted and so far so good - seems to have resolved another issue that when boiler turned off at boiler switch it continued to run (unless fans designed to operate that way).

looks as though we may be able to use wiring from programmer to pump (together with a new feed from boiler/programmer mains switch) to connect pump to boiler directly without running a new cable. not too sure about this as everything working ok now so do not really want to disturb and as I have not had heat exchanger problems with the incorrect wiring in 5 and a half years which is apparently the consequence of no pump overrun.

thanks for all the input - at least I have a better understanding of system.

pcb was £118 new - thanks for link to ebay site but as cost between refurb and an immediate new one not that great, thought I would get job done

[TheBoy]

The basic flow should be:

Timer demands heating

Stat says heat required

Valve opens (or moves position if a Y plan), switch in valve then calls for the boiler to fire

Boiler starts pump

Boiler fires


Key thing is that the boiler does not know if the pump is running. It will have an internal trip which kicks in if the water temp in the heat exchanger gets to high (on a Suprema I think the light flashes when this happens)

Which light it is is in the manual, but it doesn't need reseting - it assumes the water is hot, and runs pump until its cold enough, then relights.

So failed pumps just show up as no heating.  But a failed pump is normally easy to spot by feeling pipes as it heats from cold.

The PCB, mostly its dry joints (which by time of failure are burnt boards) ime, and can normally be easily fixed.  Maybe my PCBs haven't lasted long enough to kill the caps .  Invariably, pcb faults cause boiler lock-out.


A bang with rubber mallet can start a sticky pump, but is a short term fix!

[pscocoa]

I had an issue with one of my motorised valves that the valve would occasionally close when the thermostat is satisfied, but the microswitch would jam closed, meaning that the boiler is working into the bypass circuit (which, in my case, includes 2 bathroom radiators, so the boiler didn't get unduly upset).

If there is little or no heat load on the boiler in this state I could imagine it might lockout. Waggle the thermostat and the microswitch might unstick.

Failing that is the pump starting reliably? Could be that the capacitor is failing (it's in a pretty hostile environment) and the motor isn't starting reliably.

If the boiler starts OK the only thing on the PCB that might be suspect is the relay that controls the pump perhaps? Certainly not worth changing without further diagnosis IMHO.

Kevin

Thanks Kevin - our posts crossed - pump is not wired to boiler as it should be but has been like that since installation - I was not getting lock outs just this "burner off" signal with fans running and nothing happening.

[TheBoy]

I am assuming this is a conventional indirect heating system with boiler, hot water storage cylinder & feed & storage tanks in the loft/above the cylinder? If so, check that the ballvalve supplying the heating system (smaller of 2 tanks) hasn't become jammed shut & the tank still has water in it? :-/

yes -system is as you describe but it is working fine right now and since about 5pm.

Point tp consider also is in MDTMs post re. internal trip - question would the internal trip generate a lock out /red light or just cause the boiler to hang in burner off mode?

Lockout on suprimas (red flashing) is usually always pcb.

[henri]

have followed this thread with interest as I had a similar problem a few years ago,however I did;nt have the benefit of the oof members then.
Have to say the wealth of help and info on all matters whether car related or not is fantastic,keep up the good work . Oh and to you pscocoa I feel I should apologise for my flippant remark,hope your problem is now history   

[pscocoa]

have followed this thread with interest as I had a similar problem a few years ago,however I did;nt have the benefit of the oof members then.
Have to say the wealth of help and info on all matters whether car related or not is fantastic,keep up the good work . Oh and to you pscocoa I feel I should apologise for my flippant remark,hope your problem is now history   

no need to apologise Henri - the depth of OOF advice is considerable and not always appreciated at first glance. I suppose on here you have people who try to understand technical faults of all types whether out of interest or for cost saving or avoiding getting mugged by those that offer parts and services - "professionally".

Just returned from Reading v Leeds , 0-0 - should have stayed at home with the boiler I think - (old boiler if she cannot see over my shoulder).

on a separate note - I heard that Stihl Viking were selling unused display lawnmowers - not sure if I had been fotunate to be allocated but it turned up today - £200 for a decent self propelled about £250 under book so that offsets the pcb expense I suppose in a roundabout way. Amazing piece of kit.

[pscocoa]

Just a bit of info that may save someone time and trouble. If you get the dreaded lock out situation on the Suprima HE check for a frozen condensate pipe outside the house. This will be quite common at these temperatures. Going to get some lagging now it is cleared again. Might save you call out fees even if insured as frozen pipes often not covered by policies

New PCB cleared previous problem (original post) by the way