Boiler advice

[Brambles]

Of the three recently fitted, two were in a system to our design and one was a customer free issue. In the later case, on the day, the Customer provided a much larger boiler than they originally proposed - so it could no longer be concealed within the kitchen fitments.

On one if the systems to our design, we made a mistake with the incoming flow rate. We measured it at 30lpm, but in hindsight we think that Thames Water were working on a repair and the flow was artificially high - in reality it is 20lpm, which is too low to deliver the blended hot water to two showers. We will fit a pumped accumulator in the New Year.

My experience of large domestic - 40kw plus boilers are that in general terms they need to within 20m of the incoming gas supply - with the majority of the gas pipework in 35mm and you need incoming flow rates of at least 30lpm - that is purely my view from getting an installation that delivers at low risk of non performance. My go to solution for non performing Combis is a pumped accumulator.

From the Customer perspective - the normal comments are - it is much noisier that my old boiler and it is a lot bigger than I expected.

I try to treat large Combi’s as I do air source heat pumps and take the Customer to see an operating installation first. For airsource around 50 percent decide against it on the grounds of noise.

I hope these comments help

From an installer perspective - if they cannot tell you on the first visit about supply suitability (gas) and routing, go elsewhere. Similarly on incoming flow rates, it needs to be above the boiler spec with a decent margin.

Please don’t read this as being against Combis. I am not, but from an installers perspective I don’t want disappointed customers

 

[John.g]

On this basis I hope you can see my conundrum. I have had 3 different boiler engineer come to my house and tell me 3 completely different things, which is why I am researching it myself.

So based on the likelihood of limited gas supply (yet to be determined) would you suggest a storage combi, if sticking to a no tank solution?

What were the customers not happy with? Flow rates?

One of the recommendations above is a Viessmann 111W. Based on what I read, this has a 45 liter storage tank and has a extra circ pump that circulates cold water through the heat exchanger and into the top of the cylinder so assuming this cylinder is heated to 60C then this boiler will (by my calcs) give the equivalent of a 160 liter conventional hot water cylinder at 60C so should supply 20 LPM at a deltaT of 35C for around 12 /13 minutes, before reheating required which should take around 5 minutes. Or, will supply 14.33 LPM continuously.

 

[Russtcm]

One of the recommendations above is a Viessmann 111W. Based on what I read, this has a 45 liter storage tank and has a extra circ pump that circulates cold water through the heat exchanger and into the top of the cylinder so assuming this cylinder is heated to 60C then this boiler will (by my calcs) give the equivalent of a 160 liter conventional hot water cylinder at 60C so should supply 20 LPM at a deltaT of 35C for around 12 /13 minutes, before reheating required which should take around 5 minutes. Or, will supply 14.33 LPM continuously.

Yeah it’s on my shortlist but the 8000 45 has a similar flow rate and is a much neater unit. Yes it will need more gas but assuming I have the required gas flow then I think the 8000 is probably my preferred choice.

 

[Russtcm]

Ok I have chosen my boiler. Thank you very much for all your help. It was much appreciated and one of the highest response levels I have ever had on any forum!

My next question is on radiators. All mine seem to get nice and hot with my current 35 year old potterton but I suspect most of them are the same age. Some will be newer from 2001 as there was an extension done around then but still old obviously.

Should they be changed as a matter of course at the same time?

 

[ShaunCorbs]

That’s personal preference but you will have to change them later on depending on age can’t say how long they will last could do another 10 years might do 1 year if there functionally I would leave aslong as they heat the rooms

 

[Russtcm]

That’s personal preference but you will have to change them later on depending on age can’t say how long they will last could do another 10 years might do 1 year if there functionally I would leave aslong as they heat the rooms

I would probably prefer to do them at a different time from the boiler. Maybe in the summer so that I don’t have a double whammy with the cost. A good flush and a filter installed should protect the new boiler I guess.

 

[Russtcm]

Probably obvious but do combi boilers modulate on the hot water side as well as the heating. Presumably they don't use all of their "power" all of the time on that side either, if only a tap is lightly turned on?

 

[John.g]

Yes, AFAIK they do but normally a flow switch on the DHW side is arranged to to cut out the boiler or something like that corresponding to the minimum turn down of the boiler, the reason being I presume to prevent the HW running hot and cold with a very low flow demand and possibly for boiler Hx protection as well.

 

[Russtcm]

Ok. So I have had my 8000 45 combi installed and there has been no issue with either the gas supply or the water flow as both exceed requirements where I am. My showers are transformed into amazing power showers, really cannot believe the difference, so the hot water side is flawless.

On the heating side, I have a query for anyone that has specific 8000 experience...my heating side is set to 75 degrees and it seems to build up to it in stages. So the house was freezing after the install down in single digits centigrade. My expectation was that the boiler would heat up to 75c on heating side and hold it there until the thermostat in my hallway cut it off at the desired temp. However it seems to heat up to 50 odd, then 60odd and I have seen it go into the 70s once (not standing looking at it all day). The plume stops in between so it is going off...should it do that?

The radiators seem to get hot and then cool and then hot again, rather than it just remaining even. As the day is going on, it might be getting better but not sure yet so thought I would ask if any of this make sense?

 

[John.g]

Your expectations should be met.
Looks as if the boiler is cycling, can you open up all your rads, zone valves, TRVs, whatever fully, and see the boiler reaction, also can you see what the minimum output is on CH,. Even though you shoiuldn't have to do it IMO, you may be able to range rate the boiler on CH to 25kw or whatever the total rad output is, what does your installer say?.

 

[Russtcm]

Looks as if the boiler is cycling, can you open up all your rads, zone valves, TRVs, whatever fully, and see the boiler reaction, also can you see what the minimum output is on CH,. Even though you shoiuldn't have to do it IMO, you may be able to range rate the boiler on CH to 25kw or whaever the total rad output is, what does your installer say?.

The boiler has a 35KW output on the heating side but can go as low as 5.1KW and I have 18 rads, so this shouldn't be an issue, I wouldn't have thought.

I called Worcester this morning and they sent out their engineer but tbh, he didn't even know how to get into the installer setting on the LCD display. He hadn't seen one of the 8000 yet and I had to show him how to access and change the settings. He said that there are no error codes so it is fine but given he didn't know the first thing about the boiler, I am not convinced.

Is it possible, given the modern nature of this boiler, that it is "learning" what my house requires in terms of output and will settle over a few days?

 

[John.g]

The boiler should fire up and remain running until either heating demand satisfied or boiler minimum output of ~ 5kw is greater than the heating load, in which case the boiler will cycle, I would get the installer back and see if the pipe work etc is connected properly. Surely there were some commissioning checks carried out.

 

[Russtcm]

The boiler should fire up and remain running until either heating demand satisfied or boiler minimum output of ~ 5kw is greater than the heating load, in which case the boiler will cycle, I would get the installer back and see if the pipe work etc is connected properly. Surely there were some commissioning checks carried out.

The installer did do the commissioning checks and it was him that said something was wrong initially. He wanted to get Worcester out to see it as he feels it’s a fault with the boiler and has been told there is a software fault that can cause this. However the reset that normally fixes it, is not doing so in my case.

As it was late in the day yesterday, I called Worcester this morning.

Think I’m going to need to call them again and just say they need to send someone that actually has experience of this boiler.

Pretty poor that one of their own engineers doesn’t know how to access the engineer section on the boiler if you ask me.

 

[Owen__]

Hi Russtcm,

Did you get this issue resolved - I have some similar issues with a WB 8000?

 

[Russtcm]

Hi Russtcm,

Did you get this issue resolved - I have some similar issues with a WB 8000?

Yes I did. I spent a lot of time watching the boiler in the service menu to see what mode it was going into. It turned out that it was going into hot water mode every time that anyone or any appliance used cold water in the house. I have very high water pressure and flow where I am and the conclusion was that the back pressure when the cold water was switched off was activating the hot water mode and therefore interrupting the heating. The solution was to fit a non return valve and damper.

Since then it has worked perfectly.