Worcester Bosch Greenstar 8000 Life problems....Or are they???

[snb1]

Yes, sorry, that's still the case and since there doesn't seem to be any solution, like many other, I'm stuck.

i look after loads of these boilers, and for yours not to work means that you either not checking what has been suggested or you don't understand what has been asked. Any competent heating engineer would be able to solve it fairly quickly.

 

[snb1]

I have a relative with the open vent (regular) version of this boiler. At times it has been a very frustrating and confusing machine. The problems are nowhere near as bad as yours. But several times I've seen it stall at about 45C for more than twenty minutes, when the set point is 67C. When I've brought up the info screen, the modulation it is between 10% and 20%. It just seems to be fannying around doing nothing. The thermostats and controls are the most basic type, so there is nothing fancy going in the background which would interfere with it. After twenty minutes or so I gave up so I don't know how long it took to resolve.

On your boiler, 1-b8 and 1-c2 should show you the actual modulation and pump outputs. Although, in my experience it doesn't really shed much light on what is going on. It's probably worth trying though, just to get some background information.

on the heat only version the pump is not controlled bythe boiler. Many installers set the pump on modulation and this just causes issues. Set the pump speed to maximum ( fixed not modulating). re check system balancing of radiators ( fully close all lockshield valves and then open 1.5 turns downstairs and 1.0 turns upstairs). make sure the auto bypass valve is set at around 4 or fully closed. If the system is trying to heat the hot water at the same time the radiators then you will encounter problems. Always set system to heat the hot water for at least 30mins before the heating comes on.
If any radiators struggle to heat up then it could still be trapped air the system ( to get this out close all rads off apart from 1. fully open both lockshield valve and trv and run until nice and hot. then move on to each rad in turn. once all have been cleared of any air you can re balance the system. It only takes a small amount of air to stop a system circulating the water around certain sections.
I have assumed that trv pins on all your rads operate correctly

 

[MNW67]

on the heat only version the pump is not controlled bythe boiler. Many installers set the pump on modulation and this just causes issues. Set the pump speed to maximum ( fixed not modulating). re check system balancing of radiators ( fully close all lockshield valves and then open 1.5 turns downstairs and 1.0 turns upstairs). make sure the auto bypass valve is set at around 4 or fully closed. If the system is trying to heat the hot water at the same time the radiators then you will encounter problems. Always set system to heat the hot water for at least 30mins before the heating comes on.
If any radiators struggle to heat up then it could still be trapped air the system ( to get this out close all rads off apart from 1. fully open both lockshield valve and trv and run until nice and hot. then move on to each rad in turn. once all have been cleared of any air you can re balance the system. It only takes a small amount of air to stop a system circulating the water around certain sections.
I have assumed that trv pins on all your rads operate correctly

It is definitely the heat only version of the boiler. There is a very powerful (245w) older style external Grundfos pump which is set to 2 out of 3. In the end, I just turned up my relatives boiler to 77C and we put the heating on an hour earlier than with the old boiler. The house now gets really warm and all the radiators eventually get really hot. Also all the radiators heat up evenly. We are happy that the engineer who fitted the new boiler did an excellent job of balancing a large and complex system. I wouldn't think my relative will want me to alter any of that.

But once the radiators have gone cold they take ages to heat back up again so it still can be very confusing.

There is no doubt that this boiler spends a lot of time at a very low modulation level when the flow temperature is nowhere near the set point temperature. I have seen this with my own eyes. Why might that happen? I can't understand why it doesn't just get on with the job. It's very strange! But we've found a way to make the house warm now and that's what really matters. The problem is when it cools down it takes a lot longer than the old boiler to reheat.

I was wondering whether it might be because the difference between flow and return is much less than the 20C that is suggested for modern boilers. It is more like 6C or 8C when the boiler is close to the set point. Could that mess with the modulation?

The engineer who fitted the new boiler said the system was as clean as a whistle and that he'd never seen one so clean.

As a final question, why might heating the hot water and radiators at the same time cause this sort of problem? I've never had any issues doing that with any boiler in the past.

 

[BlueLoo]

...... We are happy that the engineer who fitted the new boiler did an excellent job of balancing a large and complex system. I wouldn't think my relative will want me to alter any of that.....

I think the poster above is correct.
Hopefully you get this sorted.

 

[MNW67]

I think the poster above is correct.
Hopefully you get this sorted.

Before my relative starts altering the system, some more detail might be helpful, of what you think might be wrong with the balance. There are 4 zones, 3 pumps and 31 radiators. The engineer spent a very long time setting it up. The radiators all heat up evenly. There is no air in the system or blockages. The system is spotlessly clean. There is plenty of flow. My relative has decided it is liveable, just a bit frustrating that a new boiler often doesn't heat as effectively as one from two generations ago. And that is because it is often idling below 20%, when it is nowhere near the set point.

 

[BlueLoo]

Before my relative starts altering the system, some more detail might be helpful, of what you think might be wrong with the balance. There are 4 zones, 3 pumps and 31 radiators. The engineer spent a very long time setting it up. The radiators all heat up evenly. There is no air in the system or blockages. The system is spotlessly clean. There is plenty of flow. My relative has decided it is liveable, just a bit frustrating that a new boiler often doesn't heat as effectively as one from two generations ago. And that is because it is often idling below 20%, when it is nowhere near the set point.

3 pumps?

Have you noted this in the chat before?

 

[MNW67]

3 pumps?

Have you noted this in the chat before?

Yes

and No

I am not the OP. I only joined the discussion yesterday, by replying to the OP, because I thought our experience might be helpful to the OP. I wasn't actually seeking any advice. There is nothing wrong with the radiators, the bypass valve or the balance of the system. It has been methodically and painstakingly set up. When the boiler decides it actually wants to fire up fully, the system works perfectly. The problem is half the time the boiler seems to just sit there idling, at less than 20% power, when it is miles below the set point. So, it takes twice as long as with the old boiler to heat the house. This is in line with the problem the OP is experiencing, with the same boiler range.

 

[snb1]

Yes

and No

I am not the OP. I only joined the discussion yesterday, by replying to the OP, because I thought our experience might be helpful to the OP. I wasn't actually seeking any advice. There is nothing wrong with the radiators, the bypass valve or the balance of the system. It has been methodically and painstakingly set up. When the boiler decides it actually wants to fire up fully, the system works perfectly. The problem is half the time the boiler seems to just sit there idling, at less than 20% power, when it is miles below the set point. So, it takes twice as long as with the old boiler to heat the house. This is in line with the problem the OP is experiencing, with the same boiler range.

The reason for the boiler sitting at 20% power or idle when not at set point is due to a couple of factors.
1 being a zoned setup with a boiler that is probably way to big for the job. ( causes flow and return temp differential to be too great and boiler reduces power or goes into waiting mode)
2, pump speed needs to be on speed 3, but pretty certain that a pump more than 10 years old will not be spinning as fast as it should be and even on speed 3 would be less than new one on speed 1. ( causes flow and return temp to be too large so boiler reduces power or goes into waiting mode)

Normal solution is check actual heat demand and reduce max power to match, and fit a pump that can pump enough volume.

 

[MNW67]

The reason for the boiler sitting at 20% power or idle when not at set point is due to a couple of factors.
1 being a zoned setup with a boiler that is probably way to big for the job. ( causes flow and return temp differential to be too great and boiler reduces power or goes into waiting mode)
2, pump speed needs to be on speed 3, but pretty certain that a pump more than 10 years old will not be spinning as fast as it should be and even on speed 3 would be less than new one on speed 1. ( causes flow and return temp to be too large so boiler reduces power or goes into waiting mode)

Normal solution is check actual heat demand and reduce max power to match, and fit a pump that can pump enough volume.

Thank you! That sounds very promising. The boiler is probably the right size for the whole house but must definitely be far too big for a single zone - even the main living zone. I will have a look at all this next time I am there. Would there be any indication on the display for me to check when it goes into waiting mode or reduces power?

EDIT: Just a quick follow up. Say we try it at 50% output. Will the boiler still start at 75% output for ten minutes? If so, would that be 75% of the maximum boiler output or 75% of the reduced (50%) output?

 

[snb1]

If you drop the max power then everthing else works off that reduced output. Don't be afraid to drop the power to 50% and see how it goes.

The amount of properties i go to that have a boiler that is more double the size needed is far too many. This then combined with zoned systems doesn't work well with the modern boilers which need high flows through their exchangers etc.

We have had this issue for many years especially with the heat only boilers as they don't have internal bypasses or are able to control the pump speeds.
Vaillant 400 series boilers were prone to these issues. we used to drop the output down to half and see if the customer complained anymore. 99% of the time they couldn;t believe what an improvement.

As soon as you can stop a boiler going into waiting periods the greater the net heat output is. max power for 3 or 4mins against 30 mins at 50%.

Depending upon which room thermostats you have can also make a difference. If they are programmable honeywell then we can alter the background settings to stop them switching every minute to every 5 mins. this also has a huge effect