I have a low capacity boiler with a "cold" case .
It is designed so that after the boiler switches off, the pump continues for a short while to dissipate the heat.
This is by circulating water through a restricted pipe that bypasses the two motorised valves ( for C/H & Hot water )
The problem is that the pump continues for a long time before it eventually switches off.
Is it likely to be a simple sensor that detects the temperature of the returning water that has failed?
I would like some idea before I call in an "engineer" or maybe a gas boiler maint operative.
I am expecting a suck teeth, old boiler tactic :-(
|
Has the length of time changed? or is it happening only now in the winter because the boiler thinks it is smart and output temperature has increased to cope with low temperatures?
From your description 'a short length of pipe' as a bypass would give it no way of adequately dissipating the heat and therefore take quite sometime to cool down - Can you not arrange the system so flow is maintained thro a 'bypass radiator'. I would start by checking what the actual flow and return temperatures are, normally and when on overrun.
I have just reread your OP and see that it is possible to interpret what you have written 2 ways -
1 the bypass bypasses the the motorised valve and allows flow thro the radiators
2 the bypass 'short circuits' the flow and return pipes of the boiler
Last edited by: sherlock47 on Thu 9 Jan 14 at 07:34
|
>> Is it likely to be a simple sensor that detects the temperature of the returning
>> water that has failed?
Could be. Might be that the pipes are furred up, the boiler might be furred up, could be low on water, might be that the valve on the bypass pipe circuit needs to be opened up, might be a setting in the boiler controls.
The only thing you do know is that the pump is working.
|
Also check (if the bypass is is as my option 1 above), is there somewhere for the water to go (flow) - have you a radiator thathat is always open when all the TRVs turned off. Have you turned the byoypass radiator off bymistake?
Is there actually any flow? which is why monitoring flow and return temps will give you a good clue as to what is actually happening.
>>The only thing you do know is that the pump is working.<< are you sure it is pumping?
Last edited by: sherlock47 on Thu 9 Jan 14 at 07:53
|
The system has been in place for quite a few years and appears to be working normally except for this running on situation.
Nothing has been altered by human hand.
The bypass allows a flow to circulate back to the boiler so no radiators are involved in dissipating heat so TRVs etc are not involved.
A while after the boiler has shut down I have been able to feel the pipes and all are cool enough to handle and keep hold of so the heat dissipation process still works.
The boiler "system" seems to believe that the returning water is too hot and thus continues the cooling circulation. This is not just for a few minutes but for at least an hour but I have not timed its total duration.
|
FWIW, Henry, last year when our boiler kept running on, it was because the paddle (?) in the motor-valve had become too stiff for the motor to operate it. The valve could be moved manually, and at one point, could only be moved with the aid of pliers.
Several different engineers came out (BG!) and temporarily freed it up but, in the end, one clued-up young bloke said he'd replace the paddle. Apparently, this was such a common problem that BG were now simply replacing the paddle rather than the whole valve.
|
I have a conventional system with a hot water tank and two motorised valves - one for HW and the other for CH. The pump and valves are with the tank in the airing cupboard.
Every now and again the pump continues to run and its the the micro switch in the HW motorised valve.
So the timer tells the CH or HW circuit to close. Motor operates in valve and closes, operates micro switch which cuts off power to pump and boiler.
In my case micro switch is dicky so valve shuts but pump still runs. There is a manual overide on valve which if you move a few times kicks he micro switch into action.
I did manage to obtain a few micro switches via the manufacturer and have probably replaced about 4 in nearly 20 years. For some reason it is always the HW circuit.
Sometimes the motors in the valves can play up with some valves having easily replacable motors.
|
FC
Your system set up seems very much like mine.
I have changed micro motors on the Honeywell valves before and played games manually operating the override to get the pump/ boiler to start up.
I will investigate the valves and the manual override.
|
That's interesting FC. I have had the blasted pump running all night at times. No doing it at the moment. I did check the valves were working but hadn't twigged to the switch in the actuator.
I have mentioned this to two heating engineers, during boiler service and when one came before Christmas to change some leaking auto bleed valves, neither has done any more than check the control wiring and pronounce it OK!
I am also suffering kettling, very intermittent and unpredictable, but sometimes when neither how water or CH circuits are on. The last plumber put this down to the absence of a bypass! Leaving the HW valve open manually overnight has reduced but not eliminated it.
|
|
Another suggestion for checking the micro switch here. Most valves only have a 5 year lifespan so either change the switch or just swap a new valve head on. (Unless they're Danfosss, who insist you buy an entire new valve and then throw half of it away.)
|
|
Over several years we seemed to go through motorised 3 port valves like sweets. Less so now for some reason although now I've opened my BFG I hate to think what will ensue! Every plumber I know now fits 2 No. 2 port valves instead, but they can all be troublesome.
|
>> Over several years we seemed to go through motorised 3 port valves like sweets. Less
>> so now for some reason although now I've opened my BFG I hate to think
>> what will ensue! Every plumber I know now fits 2 No. 2 port valves instead,
>> but they can all be troublesome.
The two port valve and the three port valve argument has been going on for years, and like fashions one or other is in vogue.
The main argument against two two port valves is that you need to install a by pass loop for the pump overrun, because you can get into the situation where both valves are off unless you have modern microprocessor programers.
|
>> The main argument against two two port valves is that you need to install a
>> by pass loop for the pump overrun, because you can get into the situation where
>> both valves are off unless you have modern microprocessor programers.
>>
No sure about that argument.
The bypass loop in my system is a simple installation.
Teed off in 15mm via a stopcock ( flow selected and the crotch handle removed) and then the pipe continues to the boiler.
I am vary wary of " plumberspeak " especially after quite a few years ago a recommended guy gave me all techno babble " old cylinder, boiler etc £2k to replace blah blah blah.
After he departed I then switched brain on, thumped the header tank ball valve and all worked fine. A new washer in the ball valve and guess what we still have the same cylinder.
I also had more than a few words with a kitchen installer who was "Corgi" approved who wanted to cut ventilation holes in my work surface. Eventually I stuffed the boiler instructions under his nose and told him to get wise!
|
|
I overcame the the valve (2 port/3 port) problems over 23years ago. I installed separate pumps for heating and and hot water. Ok so you need a couple of relays to give full control and overcome overrun issues. In that time I have replaced 2 pumps, and 1 noisy relay - but only at my convenience, not because of total failure.
|
>> I overcame the the valve (2 port/3 port) problems over 23years ago. I installed separate
>> pumps for heating and and hot water. Ok so you need a couple of relays
>> to give full control and overcome overrun issues. In that time I have replaced 2
>> pumps, and 1 noisy relay - but only at my convenience, not because of total
>> failure.
With one three way valve, In 14 years I have replaced no pumps (had to have it out to replace a leaking pump isolator tho) and one valve head (you can replace the entire plate with motor and switch on board).
In the old house I had two two way valves and in ten years I had to replace one valve servo motor.
So I don't see a problem to be overcome either way
|
I have trawled Google and it seems that the overrun fault all points to a faulty PCB in the boiler.
Initially, a while back, £120 was mentioned but now I have got the part number.
Ebay shows two, new, for sale at £30 + £3.65 p&p or £45 + £5 p&p.
Quite a difference in price and a lot cheaper than £120.
Options are
!. To buy PCB and fit it myself
2. To buy it and get a guy to fit it ( That may not go down too well but neighbour is in the building type trade so he may know someone).
3. Call ANO" boiler engineer" and risk getting ripped off re the PCB cost.
Am looking into option 1
|
|
Get a local backstreet techie to fix the pcb. Just done it here.
|
|
I think I would be getting my multimeter out and checking other stuff before I lashed out 35 quid plus on dodgy ebay parts, all based on a google diagnosis!
|
I researched further including the installation instructions etc.
PCB seems to control the pump over -run.
Cost of PCB seems to be £100 ish and illegal for me to fit it.
I am chickening out.
However further diagnosis by me.
Pump had been merrily running on ( not just for 8 mins) for a couple of hours tonight so I tried a few things.
With the control box showing C/H & HW timed to Off.
1. Manually toggled the C/H & HW zone valves but all that did was quieten things as the bypass was bypassed.
When valves returned to closed then the noise of the bypass returned.
2. Switched the mains spur box off/ on/ off/ on and the over run stopped.
Ho Hum!!!
Any thoughts on my latest findings?
|
|
Micro switch in one of the zone valves could still be fubar.
|
>> Micro switch in one of the zone valves could still be fubar.
Could be, disconnect each one in turn. The variable over-run time is a mystery tho, if the PCB was fubar it would be always on or always off.
Last edited by: Zero on Thu 30 Jan 14 at 10:14
|
>> >> Micro switch in one of the zone valves could still be fubar.
>>
>> Could be, disconnect each one in turn. The variable over-run time is a mystery tho,
>> if the PCB was fubar it would be always on or always off.
>>
Thanks for all the replies.
I will investigate the syncron motors .
They seem to cost £12 upwards so I will probably buy one to try swopping the existing ones in turn.
Always a useful spare.
|
It's not the motors, it's the microswitch inside the casing.
Whip the cover off the wiring centre for the valves and check that you're not getting 230v to the boiler switched live when the valve is in the closed position. The programmer / thermostat sends power to the valve, which opens and triggers the boiler to start.
|
>> It's not the motors, it's the microswitch inside the casing.
>>
Thanks for info.
In the wee small hours, I had a quick look at the Syncron images on Ebay and realised that with only two single tails the switches are not integral.
I will continue my quest to sort it.
|
>>Cost of PCB seems to be £100 ish and illegal for me to fit it.
Who will know...
|
>> >>Cost of PCB seems to be £100 ish and illegal for me to fit it.
>>
>> Who will know...
>>
We will but will keep quiet. Mine's a tenner.
|
Pot and kettle, Mappy.
Pat
|
Yeah ! Can't be doing with these people who change their usernames !
HO
|
>>>>Cost of PCB seems to be £100 ish and illegal for me to fit it.
Who will know... >>>
A couple of weeks ago you berated me for 'encouraging' a man on an untaxed JCB to take a little trip up a lane to remove my hedge.
...but that's different!
Pat
|
Boiler pump running on. - sherlock47
