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MickyMann

Hello everyone, I hope someone can help solve this one.
We've a 12 year old (at least) Worcester RSF280 Combi system (not condensing) which has, over the last couple of months, developed a "thud" seemingly in the house pipework when the CH pump starts up and it seems to be getting more noticeable.
It's not unlike water-hammer when a cold-water tap is turned off, except that it happens when the pump starts. Moreover, it isn't apparent when the system is heating the house in the early morning, it only happens when the system is hot and the room-stat is calling for cyclic off-on to maintain temperature.
The system sequence seems OK insofar as the fan and diverter operate then after a 12 second delay the pump starts (usually accompanied by a "thud") then after a few seconds the igniter starts and the boiler fires up.
The radiators have been bled repeatedly with little gas being present each time.
When cold the system pressure sits around 0.8bar and when hot, never exceeds about 1.4bar and it's lived quite happily like this for years.
I thought I'd sorted it out today when out of desperation I depressurised and part-drained the system to check the expansion vessel charge pressure and found it to be lower than the gauge could measure (<0.3bar) so I pumped it back up to about 0.6bar and refilled and re-pressurised the system; it seemed great for a while but as the system had been off for about an hour, when it'd been running a while and everything heated up, the "thud" returned.
I'm loathe to call in a professional at this stage as after talking to neighbours who've had various boiler problems (but none like this) I get the idea that many seem to fault-find by a "swop-it-and-see" routine iincurring substantial charges for unnecessary parts in the process which as a retiree I can ill afford.
Surely someone must have come across a problem like this and can advise, please help!
Mick
 
Thanks for quick reply,
No zone valves.
Watching the diverter, I can see the levers moving into the CH position which they do a few seconds before the pump starts.
In what way are you saying it's failed? stuck/sticking? blocked?
I sure that with this diverter I can manually lock it in the CH position and that should confirm/disprove it's the problem - would that be reasonable?
 
Thanks guys, firstly, I was wrong about the diverter being manually lockable in the CH position, it only goes to the midway position so I can't check it that way (however I could unplug the cable and temporarily connect a 240v supply to drive it fully open (I'm a retired electronics engineer so I'm confident about trying that).
Kimbo, in what way do they fail; I know the motors can be changed without draining the system (did one a few years back when it went open circuit), but from what you say it sounds (no pun intended) like its more a mechanical issue with the changeover flap-valve? or maybe the brass drive sprocket?
Lame Plumber, you seem to have missed my comment about not wanting to incur unnecessary costs, I'd be only too happy to do as you suggest but I'd like to be 100% sure that'd fix it, which is why I'm trying to find out as much as possible about the way in which it would have failed. I definitely don't want to have it changed only to be told "we'll have to change the pump now... etc" (been there with garages, got the tee-shirt (and receipts), lessons learned the expensive way). hence my seeming reluctance.
Please be patient with me.
 
Hey mickeyman you never know you might find an honest knowledgable (not swap it and see) gsr plumber out there......sounds like the diverter /3port is causing it when hot and closing due to room stat satisfied. if its circulating fine it aint the pump..
 
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Thanks guys, firstly, I was wrong about the diverter being manually lockable in the CH position, it only goes to the midway position so I can't check it that way (however I could unplug the cable and temporarily connect a 240v supply to drive it fully open (I'm a retired electronics engineer so I'm confident about trying that).

I suspect the rubber bit inside of it is worn. So it is thumbing...
1. Try operating motor separately when the pump is running and see when it does that thump.
2. Disconnect, take the motor of and try manually pushing that lever/stud. A bit of the plumbers grease or WD40 on it can be userfull.

3. If it doesn't help: drain, take the diverter off, dismantle it and replace the worn rubber parts...

4. Or (you should be quite confident with soldering :) replace that 3port valve by the 2 2port valves. The 2 port valves are MUCH MORE reliable than the 3port one.
 
like bronze_tap says its more than likely the body internals. buy a new 3 port and swap it but make sure the old nuts match the threads of the old one cos most have fine threads and some occasionally come with normal compression type threads....oh and if you do and the wires are different just ask..
 
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Hey mickeyman you never know you might find an honest knowledgable (not swap it and see) gsr plumber out there......sounds like the diverter /3port is causing it when hot and closing due to room stat satisfied. if its circulating fine it aint the pump..

Now let's not be cynical Whyme, I'm asking for advice and don't want to alienate possible helpers, however I agree, and I really would like a definite "Oh, I had that problem and *** was the cause". If I had infinite funds I'd be much more trusting and call in someone straight away but that isn't the case.
Thanks
 
I suspect the rubber bit inside of it is worn. So it is thumbing...
..........
3. If it doesn't help: drain, take the diverter off, dismantle it and replace the worn rubber parts...
.......
3. If it doesn't help: drain, take the diverter off, dismantle it and replace the worn rubber parts...
[/QUOTE]
Are the seals (rubber bits?) available separately for this type of diverter? From where?
Thanks, Mick
 
like bronze_tap says its more than likely the body internals. buy a new 3 port and swap it but make sure the old nuts match the threads of the old one cos most have fine threads and some occasionally come with normal compression type threads....oh and if you do and the wires are different just ask..
This type (Honeywell?) doesn't have screw fittings, they're push-fit with retaining clips.
Thanks, Mick
 
UPDATE: Following Whyme's, Bronze Tap's & Snowhead's advice I got myself a complete new diverter and fitted it.
It's been running for 4 hours now, systems nice'n hot and no "thuds" (so far!!! - apart from my jaw dropping when I was told how much it cost!).
For your information.....
While I was waiting for the system to heat up, I dug out a really old diverter on which the motor had burnt out and put in a new spare motor I had.
I paralleled this up with the suspect diverter I'd just removed and observed the action of the flap valves when switching them on and off together. The suspect unit was about 1-2 seconds slower when activated (to CH mode) but when deactivated (spring return operation to HW) it was at least 2-3 seconds slower. Annoyingly the lever on the side that I thought was indicating full movement actually appears to stop before the flap valves finish their moves so that had misled me into believing it was switching within the 12 seconds the boiler allows.
I tried spraying with WD40 and after a few operations it seemed to improve things a little but there's still fair difference between them. It's possible that had I done as Bronze Tap said and fully dismantled/cleaned/lubricated, it might have resolved it but I'm just as happy having fitted a new one.
So apart from all gurgling noises I've yet to bleed out (and of course the money) I think I'm going to be able to enjoy my weekend.
So thanks guys, it seems there are some "honest knowledgeable .......... gsr plumbers" out there after all.
Seriously, THANKS!!!
 
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Now let's not be cynical Whyme, I'm asking for advice and don't want to alienate possible helpers, however I agree, and I really would like a definite "Oh, I had that problem and *** was the cause". If I had infinite funds I'd be much more trusting and call in someone straight away but that isn't the case.
Thanks
Glad its worked for ya, didnt mean to come accross cynical pal. i agree about the cost some valves are really expensive..
 
So apart from all gurgling noises I've yet to bleed out (and of course the money) I think I'm going to be able to enjoy my weekend.
So thanks guys, it seems there are some "honest knowledgeable .......... gsr plumbers" out there after all.
Seriously, THANKS!!!
You are welcome!

Congratulation with the project completion! Well done!

In future don't be afraid of taking water handling bits apart. In the worst case you'll need a new one. In the best case it may be a new o-ring/washer :) And of course common sense don't leave the newly commissioned system unattended (from the leak safety perspective). Keep the bits which seems surplus today if you've got the space, you may need them when The Day After Tomorrow comes...
PS: This thread was a good comparison of the open/closed source approaches. Also I've have newer dismantled 3-port motorized diverter valve myself yet, but saw 2 port ones in the action... But the sticky stud/pin is the same problem regardless a device (thermostatic valves, motorised one, etc)...
 
Well, these grease and run attempts usually buy you a weekend or a few days/weeks before the valve starts returning in its old habits. Keeping these old valves is only good if you collect and finally dispose at a recycling place.

Done it plenty of times to bridge the time for getting replacements and there was literally a 100% return quote where the customer finally agreed it might be cheaper to replace the faulty unit.

At the end there is no way to undo corrosion or mechanical damage with reasonable efforts.
 
Well, these grease and run attempts usually buy you a weekend or a few days/weeks before the valve starts returning in its old habits. Keeping these old valves is only good if you collect and finally dispose at a recycling place.
........
At the end there is no way to undo corrosion or mechanical damage with reasonable efforts.

Very true, in one of my previous jobs (maintaining LASER cutting systems) we often had to bodge things just to keep production going until new parts arrived from abroad.
In this exercise I discovered that one of the fittings (plated steel of all things) into which the diverter pushes is badly coroded. Fortunately it's not so bad (yet) as to prevent a seal on the o-ring but it ain't gonna get any better, so I'm finally going to have to face up to replacing the boiler - probably in the summer.
Now I've just got to research which models are the most reliable/cheapest to maintain (I really hate these decisions).
Cheers all!
Mick
 
How come a divertor/three port makes a thump when the pump starts? Pump pushing against a dead head? Valve closed?
 
Pump starts running , water flow establishes. I you now picture a possible water content of 50l equaling 50kg moving at possibly 4-5mls/h and hitting a valve plate that is not firm anymore and potentially slam shutting it is comparable by you suddenly being hit by a teenager coming along on a push bike. It is quite a force as you might be able to picture.

You can simulate that with some two port valves if you ignore the arrow.
 
Basically flow of water hitting against a lose valve plate? Why isn't the valve open if the pump is running?
 
Basically flow of water hitting against a lose valve plate? Why isn't the valve open if the pump is running?

Because the boiler control expects the valve to have completed its move within a finite time (12sec in this case) and then it starts the pump. In my system the sluggish mechanism was delaying the closure. Hence "Thump".
It all seems so obvious now.
Mick
 
If you take the actuator off and try to switch by hand you will most likely get your thump at any time as long as the pump is going. Some of those three port valves are pretty prone to this. Especially if the pipes are well sized.
 
Basically flow of water hitting against a lose valve plate? Why isn't the valve open if the pump is running?
You know that on a two port valve the valve gets pushed open by the flow and shut by the actuator. On some three port valves this is just the other way round.
Hence simulating with a wrongly fitted two port valve.

Normally the actuator does not allow a slam shut. But once the mechanics are slack this does not work properly any more.
 
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