Any ideas if I might be missing something? Worcester Greenstar 28i junior, hot water runs for 5 to 10mins then boiler flame cuts out and it over heats. I can hear the main heat exchanger kettling and banging for a few mins, boiler tries to fire 3 or 4 times, then it fires up and hot water runs again for 5 or so mins. Boiler is about 8 years old, cpa all good, fan test point -5.5 mbar, central heating water all seems clear, runs fine on max test mode, pump seems strong. Can it only be the plate heat exchanger and the main heat exchanger blocked or possibly some thing else? Cheers.
Welcome to the forum. Although you can post in any forum, the USA forum is here in case of local regs or laws
- May 23, 2015
- 35,139
- 1
- 14,996
- 113
- Member Type
- Heating Engineer (Has GSR)
. Temp of the tap water 52 constant. Then obviously cold for a while when the boiler cuts out.
B
Burger
I don't think it's been well maintained as the condense trap needed a good clean out. Would a stepper motor fault cause the boiler to kettle and over heat??
B
Burger
If you get constant HW at 52oc and boiler works fine for 5 minutes then Plate HEX isn't blocked, does it modulate correctly when it's on HW?
If it was diverter it would go down CH flow so wouldn't kettle.
Pump would be my bet, check to see if it's getting a Live when it kettles. If it is see if it's spinning/operating when it does the issue. Had exactly same issues on a Baxi/Vaillant where CH seemingly worked fine but HW played up. Baxi pump kept cutting out, Vaillant wasn't pumping it round plate quick enough.
If it was diverter it would go down CH flow so wouldn't kettle.
Pump would be my bet, check to see if it's getting a Live when it kettles. If it is see if it's spinning/operating when it does the issue. Had exactly same issues on a Baxi/Vaillant where CH seemingly worked fine but HW played up. Baxi pump kept cutting out, Vaillant wasn't pumping it round plate quick enough.
B
Burger
It could be a weak pump, try stopping with a screwdriver, or test the resistance of it.
Mastermixlee
Gas Engineer
Inject some f5 or f3 into the boiler through the bleed point (isolating the ch system isolation valves on boiler) and run the hot water tap for 20 mins to half hour. Will give a good clean out of plate and main heat exchanger and will likely solve it.
Normally would put the temp clamps/probes across plate inlet and outlet as has already been suggested above first though. And a non either some probes from multimeter or non contact voltage detector on the lead to the pump to confirm power supply is consistent to pump.
Normally would put the temp clamps/probes across plate inlet and outlet as has already been suggested above first though. And a non either some probes from multimeter or non contact voltage detector on the lead to the pump to confirm power supply is consistent to pump.
Mastermixlee
Gas Engineer
Many a time. Works a treat. Like a mini powerflush for the heat exchangers. Obviously drain out afterwards.
Is the boiler modulating? Keep an eye on the inlet pressure see if it goes up and down.
Remove the motor from the DV and run it round the heating for a bit.
Undo the screw on the pump stick a screwdriver in it if you can stop it pump is shot if it tries to break your screwdriver end off it's all good.
Get it hot and then link out the flue O/H stat.
Remove the motor from the DV and run it round the heating for a bit.
Undo the screw on the pump stick a screwdriver in it if you can stop it pump is shot if it tries to break your screwdriver end off it's all good.
Get it hot and then link out the flue O/H stat.
- May 23, 2015
- 35,139
- 1
- 14,996
- 113
- Member Type
- Heating Engineer (Has GSR)
Okay so if it's not modulating what would cause that and you say link out the o/h stat, why?
Mastermixlee
Gas Engineer
Can be dhw temp sensor, PCB or fan PCB that can cause it not to modulate. Would need to find out from manufacturers expected resistance range of thermistor to temperature relation & to find out expected voltages to fan
If it's not modulating then I'd look at thermistor. Generally pcbs on Worcester are not that bad the fans are shocking but if they go they go properly.
Disconnect the FLUE o/h stat. I believe it is linked on the same as the o/h and aps. I've had a couple fail in the past when they start to get hot. They can be tricky to diagnose as they are intermittent.
Mastermixlee
Gas Engineer
From your description I'm still of the opinion that it's gonna be restrictions causing the issue. As if it wasn't modulating then the hot water wouldn't likely remain at 52degrees.
And flue o/heat stat wouldn't cause it to bang and crash like you've described.
I'd check the thermistor ranges anyway and then do the old f3/f5 trick.
And flue o/heat stat wouldn't cause it to bang and crash like you've described.
I'd check the thermistor ranges anyway and then do the old f3/f5 trick.
If it was a restriction I would imagine it would happen when the boiler is running on max not so much after it had been running for a while.
My guess would be pump dodgy but I thought I would mention everything else so they can check it all instead of going to the job seeing if its modulating then coming back on here then checking the pump and coming back on here.
Mastermixlee
Gas Engineer
Yeah wasn't going against you so much just trying to stop op wondering where to start with all of it lol.
They mentioned they'd checked pump and that was all ok...unless I'm mixing posts up... Quote possible it's Friday night after all 😀
Thanks for everyone's input. Most appreciated.
Yes I did see the pump running when it was doing it, and it couldn't be slowed with a screwdriver, but I suppose there is a chance it may have briefly failed for a second, so I'll test it with a voltage pen to see if it briefly looses power. That would explain the kettling and it shutting down. I'm not sure about the oh stat failing as it was over heating. I'll check gas pressure to see if it's modulating. I was thinking it would be a plate blockage as it only does it on DHW and not in max service mode. Surely the only difference there is the plate heat exchanger being used in DHW mode.
Yes I did see the pump running when it was doing it, and it couldn't be slowed with a screwdriver, but I suppose there is a chance it may have briefly failed for a second, so I'll test it with a voltage pen to see if it briefly looses power. That would explain the kettling and it shutting down. I'm not sure about the oh stat failing as it was over heating. I'll check gas pressure to see if it's modulating. I was thinking it would be a plate blockage as it only does it on DHW and not in max service mode. Surely the only difference there is the plate heat exchanger being used in DHW mode.
Okay went back to check a few things today,
: Linked out over heat stat and still over heated, linkef out flue over heat stat, still over heated.
: Temps going in and out plate to plate where about 28 degrees different. Got up to 76 in 47 out before it shut down.
: Powe to the pump is constant until it shuts down, then it pulses for a while before the fan comes on and it fires.
: Gas pressure went up and down, but only by 1/2 a mbar so thinks it's modulating. The water flow isn't very high so to me it sounds okay. When the flow is reduced at the tap it does modulate right down.
Surely it can only be the plate to plate do you think??
: Linked out over heat stat and still over heated, linkef out flue over heat stat, still over heated.
: Temps going in and out plate to plate where about 28 degrees different. Got up to 76 in 47 out before it shut down.
: Powe to the pump is constant until it shuts down, then it pulses for a while before the fan comes on and it fires.
: Gas pressure went up and down, but only by 1/2 a mbar so thinks it's modulating. The water flow isn't very high so to me it sounds okay. When the flow is reduced at the tap it does modulate right down.
Surely it can only be the plate to plate do you think??
Last edited:
- May 23, 2015
- 35,139
- 1
- 14,996
- 113
- Member Type
- Heating Engineer (Has GSR)
Surely it's about right though? If your HW is around 55oc then return isn't going to be much less is it.
Plus boiler will modulate at that.
- May 23, 2015
- 35,139
- 1
- 14,996
- 113
- Member Type
- Heating Engineer (Has GSR)
water incoming temp around 15 dc plus the 28 dc rise give you 43 dc hot water temp
normally in hot water mode the boiler wont modulate eg turn tap fully on should stay on max
normally in hot water mode the boiler wont modulate eg turn tap fully on should stay on max
Sorry so are you saying it sound like the plate needs replacing? Water at the tap was about 53/55. Is it scaled up do you think?
If water is coming out at that temp doesn't seem much wrong with plate IMO.
Isn't so easy on the Juniors, you have to take the hydraulic block out if I remember correctly. And tbh if you ain't got a new washer pack it's going to leak.
Mastermixlee
Gas Engineer
Can get the plates out on them if you cut the hot water outlet pipe. You can then wiggle it out the back down that gap (provided you've got clearance below the boiler to do it).
Though still would of gone the f5 trick personally to do a mini clean on it first.
And obviously check the vanes on the pump too to check no debris in there.
Don't see much else that can be suggested to be honest.
If thermistors are in range, pump voltage is constant when on demand, Ch runs fine, boiler modulates down etc, pump confirmed to not be cutting out etc then there's little else that can cause it.
But without checking and confirming all the above then it'll still be guesswork.
Though still would of gone the f5 trick personally to do a mini clean on it first.
And obviously check the vanes on the pump too to check no debris in there.
Don't see much else that can be suggested to be honest.
If thermistors are in range, pump voltage is constant when on demand, Ch runs fine, boiler modulates down etc, pump confirmed to not be cutting out etc then there's little else that can cause it.
But without checking and confirming all the above then it'll still be guesswork.
The only thing that puts me off doing the f3 trick is that wouldn't work on the water side. So if that's scaled up the only thing I could do would be replace it. And yes I've changed a few by cutting a pipe and squeezing it out. I'm always reluctant to replace anything with out being fairly positive it'll sort it, I do hate these kind of faults!
Mastermixlee
Gas Engineer
Whilst I've had plenty of scaled plates causing poor hot water performance I've never had scale on the dhw side causing boiler overheating, as the system side would be clear and modulate down based on flow and return thermistors.
Just my experience though.
Just my experience though.
I have had them before when the plate to plate is really scaled up and it makes all sorts of kettling noises with the boiler shutting down. It's not like that though with this one. Still not sure what to do next.
On hot water mode the modulation is carried out by the dhw thermistor. The primary thermistors are basically high limit stats and should cut the boiler out before it over heats.
It’s not about giving it to Worcester. It’s about the best route for the customer.
Sorry I disagree.
The best route for the customer is to diagnose and fix it yourself.
All the manufacturers care about Worcester especially is selling boilers they re not worried about the customers or the installers.
The best route for the customer is to diagnose and fix it yourself.
All the manufacturers care about Worcester especially is selling boilers they re not worried about the customers or the installers.
@Millsy 82. Disagree all you like. Says a lot. If the cost of me repairing is more expensive then a Worcester fix. The options are new boiler or Worcester fix. For example, there is no way a normal engineer can fit a main heat exchanger in a Junior for less then a Worcester fix priced repair.
I pretty much said.
Dont give the work to the manufacturers. They dont give it back. Yes if you install 100 Worcestershire a year they will look after you but otherwise they couldn't care less if you get work or not.
Better money going into your pocket than theres.
As for if you cant diagnose it. Speak to tech it's free and if you know what to ask which has been said on this thread you should get to the answer.
Will Worcester pay your mortgage? How about baxi? Vaillant? No none of them will YOU need to earn money as well.
If I had that attitude I wouldn’t have any work. I’m busy because I’m all about my customers.
I do and the same customers keep coming back even after a fixed price repair because I have saved them money.
I agree it can be a good move to call in the manufacturer for a fix priced repair. I have done it my self but only when I know with out a doubt it'll cost more for me to fix it. It could be very embarrassing if the fault doesn't cost a lot to repair!
With regards to calling Worcester or any other manufacturers it can be hit and miss with them. They might have the answers on a screen in front of them but I'd say not many of them have hands on experience. I might be wrong. It's easy for them to say replace this and that but this and that can cost 100's!
Back to my question though..is there more than 1 DHW thermistor??
What about when your customers want an install do you say Go with Joe blogs plumbing as he will fit you a boiler for £100 where as I will charge you £500 so you save them money then.
They ask me to quote. I quote and tell them to get 2 more in to compare. On a repair I tell them it is this much for me to repair or this much for Worcester and I only do it with Worcester because there boilers are rubbish.
Not really.
It seems that running a business now is all about saving your customers money so how is it different?
You should be charging a fair amount for a good job. Simple as that really.
I do. My mortgage is paid and I’m more than happy with what’s left. I don’t need to be greedy.
And the fact remains that this thread has been running since Friday and I’m assuming there is no answer yet? With return visits and testing g this is gonna be an expensive bill
I'm sure that's how homeserve think or bg or Worcester or vaillant or any other big company. I dont want to be greedy let's give the little guy a chance. Hahaha like that will happen.
But I’m not Homeserve/BG/Worcester or Vaillant. I’m Harvest Fields! That’s my USP!
This giving jobs to these large companies is utter madness. Why are these jobs so expensive? It's not labour charges its 100-150% mark up on materials from them that make the prices so expensive.
You say it's too expensive hand it over to them they throw parts in that cost them virtually nothing pay someone a pants wage so either way it's a win win for them.
Large companies are ruining the world all in the name of profit and you guys are just handing it over to them.
You say it's too expensive hand it over to them they throw parts in that cost them virtually nothing pay someone a pants wage so either way it's a win win for them.
Large companies are ruining the world all in the name of profit and you guys are just handing it over to them.
I’m only handing it over to them if I lose the customer and at present I haven’t lost one. It’s a no brainer to help my customer out mate. That’s how I’m built. I will never change.
I think you are entirely missing the point of the argument mate this problem has not been diagnosed with all the advice we have given. because the OP haven’t come back yet we still don’t know if it has been diagnosed if it is something that simple as the plate to plate then of course do it yourself but if it is a bigger problem then you as the engineer don’t want to be the one throwing parts at it in the hope that you repair it
Mastermixlee
Gas Engineer
I have to agree to a certain extent as for the most part I've had alot of experience working for BG.
And the number of customers I've had over the years that were referred to BG by their usual plumber/gsr with the "he said it would be cheaper for me to get the fixed price repair by BG" that end up signing up to the homecare maintenance plan (thus leaving their usual guy who saved them the money with the advice out of pocket and one less customer) is a huge percentage.
It's rare that Id go to one that was a fixed price repair job that didn't end up being a maintenance contract sign up.
But we are talking about Worcester here mate. I would never send a customer to BG. I have also worked there.
This is the problem, after all the checks I've not pin pointed the fault to be confident enough to start throwing expensive parts at it. Last thing I want to do is replace the plate to plate and find it's not sorted it, then ask for the customer for payment and tell them to get Worcester in. I think I'm going to replace the DHW thermistor ( think there is only one ) as that's not expensive and then run the F5 through it.
I know it’s been mentioned two or three times in the thread but have you actually called Worcester technical they are pretty good
Mastermixlee
Gas Engineer
Thats entirely up to you. But Worcester do also have their own maintenance plan that they offer.
Sure if you've built up a good loyal customer then by all means save them money wherever you can (as long as you have charged for your initial diagnosis/time at least first).
But if it's potentially your first visit to a new customer and you refer them straight to the manufacturers (op case may or may not be this scenario) then it's highly likely you may lose that customer in my opinion.
Also a point to note that some may already be aware of is that by funding Worcester (if you perform install work too) then you are indirectly funding Boxt (a big competitor) as Worcester are a large shareholder in this business and supply boilers to Boxt for alot lower than general installers could possibly hope for...thus being able to offer lower prices generally.
In op case I don't think all avenues have been tested enough to pass to Worcester yet. As they have now said they will do, the dhw thermistor and f5 run through is cheap and could solve the problem for fraction of Worcester callout.
If you still are struggling after that then sure go down manufacturers route (if you haven't already ran through tech help on phone with them first that is, but assume you've already done that).
Yes called them twice. Their answer is it's PROBABLY the plate to plate or a blockage, PROBABLY.. I've had better info on this site from people who actually work on boilers, which isn't surprising really.
Mastermixlee
Gas Engineer
So guessing they ran through with you the thermistor resistances etc? If yes then whilst they can go out of range with temperature rise it isnt that often.
Though for £6-8 part cost and 10 minutes work it's definitely worth a punt first.
On my first call they didn't mention any thing about testing any thermistors, just blockage. On my second call I said I'd checked the thermistors and they thought it wouldn't be that. As you say a DHW thermistor is cheap as chips and it might be going out of range, so I was thinking of replacing it just before I try to clean it with f5. I checked all the others by linking them out one at a time and it still had the fault.
Mastermixlee
Gas Engineer
If you change the thermistor and it's not solved, don't throw away the old thermistor. Keep it so if you ever get similar issue again then you can easily change out thermistor at no cost to test and confirm future diagnosis.
It's difficult to weigh up what's best. Even if I take it out and look in it I might not see anything and it could still be blocked. And it's not one of the quickest ones to take out. Plus with the cleaner I'll be cleaning both heat eexchangers and the pipe ways.
- May 23, 2015
- 35,139
- 1
- 14,996
- 113
- Member Type
- Heating Engineer (Has GSR)
That's interesting to know that they are a large shareholder in boxt.
I was going to say that eventually you will end up giving too much to Worcester that you are no longer needed and they will have there own engineers install the boilers and then there own engineers repair them and so on.
It's like these boiler diagnostics that bg now offer, when will Worcester start offering them to their customers then steal all the Worcester repairs market then if the other manufacturers follow suit which they do boom no more breakdowns unless you work for the big companies then no servicing as they will say warranties will be void unless serviced by a manufacturer approved service engineer then the next thing were all going round changing taps and unlocking toilets.
It is very scary what the jobs market will be in the future and how future generations will live in a world where large companies are more powerful than countries.
- May 23, 2015
- 35,139
- 1
- 14,996
- 113
- Member Type
- Heating Engineer (Has GSR)
It will happen. These large companies are only profit and power driven, not like the likes of me and you that want to earn enough to fend for our families but they want to take over the next company streamline and take more profits off them and so on.
My mrs watches inside the factory and you see how all the factories now have driver less forklift going round. Driverless lorries are on the way. People buy fuel from a robot (I refuse to pay at pump) meter readers are becoming obsolete due to smart meters that supposedly save us money (more like they save having to employ as many people) companies like Amazon are trialling robot deliveries in cities. In 30 years time the world will be totally different that's why I disagree with giving too much to these big companies.
- May 23, 2015
- 35,139
- 1
- 14,996
- 113
- Member Type
- Heating Engineer (Has GSR)
I dont think you get what I was saying.
Worcester is owned by Bosch boxt is part owned (45%) by Robert Bosch uk holding Ltd
So try telling me that Worcester have nothing to do with boxt.
- May 23, 2015
- 35,139
- 1
- 14,996
- 113
- Member Type
- Heating Engineer (Has GSR)
Just an update..
Replaced the DHW thermistor and it still over heated on hot water.
I then ran the F3 cleaner through it buy closing off the flow valve with the hot water tap open. Ran it for about 20 mins with the cleaner in it, left it for half hour and ran the tap again for another 15mins. It still continued to over heat as I ran the cleaner through it. Gave me the impression it hadn't worked. Flushed the cleaner out, which was quite black, filled it up to 1 bar and ran it. At first it still didn't run right, but eventually it settled down and now seems to be fine. Customer has used it for a week and said it's perfect. It makes me think the main heat exchanger was blocked.
Replaced the DHW thermistor and it still over heated on hot water.
I then ran the F3 cleaner through it buy closing off the flow valve with the hot water tap open. Ran it for about 20 mins with the cleaner in it, left it for half hour and ran the tap again for another 15mins. It still continued to over heat as I ran the cleaner through it. Gave me the impression it hadn't worked. Flushed the cleaner out, which was quite black, filled it up to 1 bar and ran it. At first it still didn't run right, but eventually it settled down and now seems to be fine. Customer has used it for a week and said it's perfect. It makes me think the main heat exchanger was blocked.
Mastermixlee
Gas Engineer
Official Sponsors of Plumbers Talk
Similar plumbing topics
- Question
- Question
- Aquafix 73
- UK Plumbers Forums
- Question
- Question
- Question
- Question
- Poll
- Czech Pete
- UK Plumbers Forums
We recommend City Plumbing Supplies, BES, and Plumbing Superstore for all plumbing supplies.
