Worcester bosch 8000 32kw Boiler

Neversurrender

Hi,
Was wondering if any of you guys can help me please.
I have a Worcseter Bosch 8000 32kw Combi boiler installed 8 weeks ago.

It is controlled using a Bosch Easycontroller smart Room stat hard wired in to the boiler.

OK so what's happening, here's an example.
Let's say the room stat is showing room temp of let's say 17c, and I put the target temperature I want the room to be of let's say 21c

The boiler starts up then after usually just a rise in room temperature of only around 0.5 of a degree c, the flame goes off, then there is a short wait of around 3 minutes, before the flame comes back on and stays on then until the desired room temp set to 22c is achieved.
So it appears the boiler doesn't modulate the first time it comes on and switches flame off after only a 0.5 degree rise in temp
But
It modulates the second time it comes on. By reducing the flow temp and burner KW to 5 kw it then stays on until that target temp of 22c is achieved.

I've had the WB engineer out 4 times, they seem to think boiler its heating up too quickly, then shuts off to avoid overheating.

We have range rated the boiler down by 50% so it acts like a 16kw boiler as they are now saying boiler is too big for the 7 rads we have.

They did say this would be case before we bought this boiler, but said the 8000+ is the best built boiler and has an extra 2 years warranty  and said it could be range rated to suit our system.

Any of you guys out there have any experience of these boilers with Easy control smart stat.

Thanks

FreeBear

For heating, a 30kW boiler will always be oversized. But if you have a cold water flow rate of 11-12l/min, it is about right for a combi.

I have a 30kW combi myself (Viessmann 050) with 9 radiators for a total of ~13kW@ΔT50°C. The boiler is range limited to 10kW and the maximum flow temperature is set to 55°C. It will only short cycle at really low flow temperatures and a TRV has taken one or more of the bigger radiators out - This will only happen after the boiler has been running for an extended period..

I'd suggest dialing the range limit back even further to 25% or even lower. Set the maximum flow temperature to 60°C. If your radiators are suitably oversized, you might even get away with a max flow temperature of 50°C.

A lower flow temperature will improve boiler efficiency and also reduce corrosion within the system.

One final thought - Have your radiators been balanced properly ?

I've adjusted my lockshield valves to get a flow-temp*0.3 °C drop across each radiator (had to turn the pump speed right down to achieve that).

Neversurrender

Hi Thsnks for the reply.

This boiler will only range limit to 50%, so 16kw is minimum.

All rads heat up at same rate, all have lock shields open to max

No trv's apart from bathroom towel radiator

Flow temp, sorry I should have mentioned is 65c currently, we've tried it at 55c and didn't really make much difference.

Albermarle

It is a long shot but do you know what pump speed it is running at ( usually 1,2 or 3)

For only 7 radiators probably a slow pump speed ( 1) could be sufficient.
If it on full ( 3) you are probably best to turn it down anyway. It can not do any harm. 

Neversurrender

Albermarle said:

It is a long shot but do you know what pump speed it is running at ( usually 1,2 or 3)

For only 7 radiators probably a slow pump speed ( 1) could be sufficient.
If it on full ( 3) you are probably best to turn it down anyway. It can not do any harm. 

Thanks

I went through all boiler settings related to pump and all I could find were pump delta settings several all numbered 1,2,3,4,5

FreeBear

Neversurrender said:

Hi Thsnks for the reply.

This boiler will only range limit to 50%, so 16kw is minimum.

All rads heat up at same rate, all have lock shields open to max

No trv's apart from bathroom towel radiator

Flow temp, sorry I should have mentioned is 65c currently, we've tried it at 55c and didn't really make much difference.

Most of the lockshields should only be open by half a turn, certainly not fully open. Having all the lockshields wide open means the water returning to the boiler doesn't have enough time to lose heat to the room. With my boiler, the return temperature is 15-20°C lower than the outgoing flow. Having cooler water flowing in to the boiler means it can condense more effectively (higher efficiency and less white "smoke" out of the flue).

Albermarle said:

It is a long shot but do you know what pump speed it is running at ( usually 1,2 or 3)

For only 7 radiators probably a slow pump speed ( 1) could be sufficient.
If it on full ( 3) you are probably best to turn it down anyway. It can not do any harm. 

The Greenstar 8000 has 6 constant pressure settings. Default is number 3, whilst 1 is the lowest and 6 way too high. Turning the pump speed down to minimum will allow more time for the water to give up heat whilst in the radiator. There will also be a lot less noise - Got my pump speed set to (almost) the lowest speed, and you can hardly hear the water circulating.

Albermarle

FreeBear said:

Neversurrender said:

Hi Thsnks for the reply.

This boiler will only range limit to 50%, so 16kw is minimum.

All rads heat up at same rate, all have lock shields open to max

No trv's apart from bathroom towel radiator

Flow temp, sorry I should have mentioned is 65c currently, we've tried it at 55c and didn't really make much difference.

Most of the lockshields should only be open by half a turn, certainly not fully open. Having all the lockshields wide open means the water returning to the boiler doesn't have enough time to lose heat to the room. With my boiler, the return temperature is 15-20°C lower than the outgoing flow. Having cooler water flowing in to the boiler means it can condense more effectively (higher efficiency and less white "smoke" out of the flue).

Albermarle said:

It is a long shot but do you know what pump speed it is running at ( usually 1,2 or 3)

For only 7 radiators probably a slow pump speed ( 1) could be sufficient.
If it on full ( 3) you are probably best to turn it down anyway. It can not do any harm. 

The Greenstar 8000 has 6 constant pressure settings. Default is number 3, whilst 1 is the lowest and 6 way too high. Turning the pump speed down to minimum will allow more time for the water to give up heat whilst in the radiator. There will also be a lot less noise - Got my pump speed set to (almost) the lowest speed, and you can hardly hear the water circulating.

OK , I only have an old fashioned separate pump outside the boiler ,and you set the speed with a button on the pump. ( by the way it is set on 2 but also on the setting where it reacts to the pressure in the system)  It is very quiet.)
I was forgetting these newer top of the range boilers have it all enclosed and digital .

Neversurrender

@Albermarle

No worries, I guess the principal  is similar, thanks for your help

Neversurrender

@FreeBear

Many thanks for all your help,

What you say makes perfect sense, I have gone round and closed all lock shields then opened about 1 full turn and all are heating at same rate

Also taken your earlier advice and reduced flow temp from 65c to 60c to see how that goes.

So far so good, but will try again tomorrow  as I can see the Mrs starting to dehydrate with all this heat

FreeBear

Albermarle said:

FreeBear said:

Neversurrender said:

Hi Thsnks for the reply.

This boiler will only range limit to 50%, so 16kw is minimum.

All rads heat up at same rate, all have lock shields open to max

No trv's apart from bathroom towel radiator

Flow temp, sorry I should have mentioned is 65c currently, we've tried it at 55c and didn't really make much difference.

Most of the lockshields should only be open by half a turn, certainly not fully open. Having all the lockshields wide open means the water returning to the boiler doesn't have enough time to lose heat to the room. With my boiler, the return temperature is 15-20°C lower than the outgoing flow. Having cooler water flowing in to the boiler means it can condense more effectively (higher efficiency and less white "smoke" out of the flue).

Albermarle said:

It is a long shot but do you know what pump speed it is running at ( usually 1,2 or 3)

For only 7 radiators probably a slow pump speed ( 1) could be sufficient.
If it on full ( 3) you are probably best to turn it down anyway. It can not do any harm. 

The Greenstar 8000 has 6 constant pressure settings. Default is number 3, whilst 1 is the lowest and 6 way too high. Turning the pump speed down to minimum will allow more time for the water to give up heat whilst in the radiator. There will also be a lot less noise - Got my pump speed set to (almost) the lowest speed, and you can hardly hear the water circulating.

OK , I only have an old fashioned separate pump outside the boiler ,and you set the speed with a button on the pump. ( by the way it is set on 2 but also on the setting where it reacts to the pressure in the system)  It is very quiet.)
I was forgetting these newer top of the range boilers have it all enclosed and digital .

Your basic external pump would cost £50-100 plus fitting with the advantage of simple speed control.

Using a genuine Viessmann part would cost me £350 plus fitting. Could get it a lot cheaper by going to a Grundfos reseller (maybe under £120). To change my pump speed means navigating the service menu to find the right option.

You have the advantage of lower cost and the option of DIY fitting. Once my warranty expires, I'm at the mercy of a Gas Safe engineer.

Lorian

Check the flow and return pipe temps on the boiler if it happens again.  balancing may have helped but it probably wouldn't have happened in the winter with more actual demand. You might have been tripping over the Worcester anti cycling.