REQ Help - Ideal Classic Combi NF80

[Gunslinger]

ok guys, please bear with me as i have not posted here before, and if i have missed any information needed please let me know.

Problem - basic
Boiler seems to have gained a mind of it's own, running central heating when nothing is calling for heat.

setup
NF80 Combi Boiler performing HW and CH duties
Honeywell independent Frost Themostat - disconnected at the moment
1x Honeywell CM67 digital programable room thermostat, connected to the NF80 as a "clock control of heating only" - i know the CM67 is a thermostat, but as far as the boiler is concerned it sees only a on/off command from the CM67 via the switching relay, so should perform as per with a timer clock.
HW is for one bathroom only with low usage
Boiler is usually set to HW+CH operations, 24hr D.H.W Pre-heat mode
Pressure gauge reads 1bar stone cold and 2bar when up to temp and in use.


Problem - more detail
system has been running fine for a number of years now, no major issues other than sticking rad thermostats (now removed) and one timer clock that died (replaced with CM67 room stat)
a few days ago, i caught it heating the rads when the thermostat was not calling for heat, so here's what i tried:
1. initially kept my eye on it turning the required temp down on the CM67 to ensure it was not going to be calling for heat, rads still came on sporadicaly
2. removed the honeywell frost stat, as it's not technically required with the CM67 fitted - problem persisted
3. turned CM67 into manual mode and set to 13 degrees - problem persisted
4 turned off the CM67 (it defaults to 5 degrees frost protection mode in this stting) - problem persisted
5. pulled the battery pack out of the CM67 - problem persisted



Basically, with both of the external heat requesting sources removed or disabled the boiler was still pushing heat (pumping) around the CH system, this was not a constant thing, it does at times switch itself off and on, but i am not sure at what temperatures.
So i switched it from HW+CH operation to HW only, yet the problem still persisted.

the only logical explanation i can think of (as the makers say there is no control in the boiler that should call for heat on the CH circuit independent of an external switch) is that somehow, the HW Pre-Heat circuit is actually firing up the pump for the CH circuit as well, making the boiler seem to have a mind of it's own controlling the CH.
I can not see any way of running the boiler in CH mode only to test this theory

Anyone got any thoughts ? or maybe seen this behaviour before ?

TIA

 

[kevplumb]

does the heating come on when you run the hot water

 

[Gunslinger]

not sure, that is something i did not test.

i will go and have a look see,

i assume if i leave the room thermostat disconnected, that when i switch the boiler on from cold the hot water pre-heat will fire up as its stone cold, this, unless i am thinking wrong should NOT turn on the CH, right ?


i've been looking through how this thing works, and i am leaning towards the idea that the Diverter valve is stuck open

i think this test of yours might show this.

be back in a little while with results


thanks for the reply btw

 

[Gunslinger]

ok thats weird ....

just went and made sure the room stat was set to off - it is, and the boiler was set to HW only - it was .... and it was also turned off at the switch next to the HW/CH control selector ... and the pump was running

turned the boiler on and it's fired up as expected ... just waiting now to see what gets warm and what doesnt

 

[Gunslinger]

ok, answer to your question...

Boiler on in HW mode only
switching on caused the boiler to fire up as expected, main burner came on - presumably for the pre-heat mode - Radiators heated up too, somewhat slowly though, but got fully hot - no HW drawn off the system at this point.

waited for it to reach normal temp and shut down ..... this took about 20 minutes, burner shut down and no pump noise is heard, so i assume the pump has shut off too

this seems a little long to me, and makes me wonder if it switching off might be the result of the overheat thermostat operation

will monitor it for a 30 minutes, then draw off some water when it is not already heating and report back



Side Note: pressure gauge is now reading 3.5 bar when in use

 

[Gunslinger]

ok, second test results, still with the boiler set to HW only

waited for a while to ensure boiler main burner was not on and Rads cooled off. before drawing off HW, but before i did i checked to see if any pump activity could be heard - none, so pump seemed to be off

turned on hot tap, and waited for hot water to come through - which it did, got nice and hot too !

Checked boiler - and main burner was on as expected

checked radiators - pump noise could be heard through the system and the rads got fully hot (cant hear pump at boiler when main burner is on it drowns out the small pump noise) - rechecked hot water from tap, and while still warm it was not "hot" so to speak - varying hot water temps is a bit of a feature of this boiler.

stoped draw off of hot water, and main burner stayed on for about 10 - 15 minutes, at which point it shut off and the pump also switched off, as no noise could be heard either at the boiler or through the system to the rads.

i've now turned it off again at the boiler - i want to wait until it's cold and see if i can hear the pump rotating again, that seems really odd to me that the pump seemed to be running even though the boiler was switched off !


so, other than the pump running when the boiler was switched off - which i will keep an eye on, the HW pre-heat mode and when drawing HW seems to be running the CH circuit as well immaterial of external thermostats, and it's my guess that the boiler isnt switching off until it hits the over heat thermostat setting, and switching back on when the pre-heat mode fires up to maintain the water temp


any thoughts ?

 

[Gunslinger]

ok, confirmed....

with everything turned off, thermostat, boiler at its switch at the bottom and the system cold....

the pump is running

 

[kevplumb]

is the diverter motoring at all

 

[Gunslinger]

not sure - going to try and look at that now and using the manual slide lever on the diverter valve see if the valve is stuck open, if it is, then the manual lever should be loose and move with no restriction - but i have to strip the covers off the boiler to get to it

 

[Gunslinger]

ok - the valve has issues !

the manual lever is loose for about 85% of its travel on first inspection.

firing the boiler up in HW mode results as before in the rads heating up - with the valve head cover removed, manually forcing the actuator arm closed solves the rad heating issue....

switching to HW+CH mode, and the valve opens fully so that the manual lever is loose across it's entire travel with no resistance, and the Rads heat up ... but, it is very slow in energising/opening

switching back to HW only mode, and the valve starts to close really slowly, and gets stuck at about the 25% closed position, leaving the radiators getting heated water... forcing it the rest of the way with a screw driver closes it and solves the problem


so i'm thinking old age has caught up with the valve, and possibly a build up of crap in the system at that point is making it too difficult for the springs to return the valve to the closed position, or the motor head is knackered slightly causing it to increase the closing resistance higher than the springs can cope with.

either way, it has to be replaced, i'll get someone in to replace it as the system has to be at least partially drained, so they might as well flush it for me too, and check the rest of the boiler over while their at it.


thanks for the help Kev, your questions made me look at it from a different point of view... i was so dreading the problem being on the logic board somewhere which would have been costly

 

[kevplumb]

no probs i think i have a book on that one if it will help

 

[Gunslinger]

no its ok, as it could do with an inspection by a qualified fitter anyway to make sure there isnt any other issues i'll get someone in to do it.

i can get the valve myself as its a standard honeywell part (stupid thing is i swapped about 6 of those diverter valves for 4 of the simple zone valves for the replacement system, not to long ago !)

but being able to book someone for a job saying, please replace this part, flush the system and perform an annual safety check is a lot cheaper than calling someone in saying "my boilers got a mind of it's own all of a sudden

 

[Gunslinger]

ok ,this one is now solved - and yes it was the diverter valve, replaced with a new one and it now works as it should, accept i have another problem (expansion essel full of water!) - will make a new post about that