BEM 5000

[BEERMONSTER]

Hi,

We have recently made some upgrades to our heating system and in the process changed our knackered BEM 4000 to a BEM 5000 unit which was purchased off ebay.

The BEM 5000 worked for a while, but we are now seeing some issues with the weather compensator stopping the boiler from firing. I have been through the issue with Danfoss and have concluded that the unit is faulty.

I know the unit is now obsolete, but wondered if anyone knew of someone who still had one (new or used) that they would like to sell?

I know there are other weather compensators out there which mix the water, but we would prefer to try and swap out the unit initially as we know it helps save money!

Cheers

Andy

 

[BEERMONSTER]

Anybody

 

[simb82]

I have an old unit here, if you want it for postage costs? dont know if works though

 

[Onetap]

They were junk when new and caused corrosion problems with non-condensing boilers.

Bin it and buy yourself a proper control system and/or a modulating condensing boiler.

 

[Boilerman2]

As above! Danfoss BEM was a pile of KACK!!

 

[BEERMONSTER]

I know the BEM unit is not the best thing out there, but better controls/new commercial boiler = a lot of money which isn't viable at the moment for our charity. As for the corrosion point, yes it will cause issues, but only if you set the response curve too low. It clearly states this in the manual!

SIMB82, I have sent you a PM

 

[hmcleod137]

I have a new boxed unit if you are still looking for one

 

[BEERMONSTER]

Thanks for the offer, but we have now fitted one of these devices.

http://www.radiantcontrol.co.uk/pro...ntrols/boiler-controls/boiler-controller-260e

Along with this controller, we have now binned the timer units in favour of 30/60/120 min boost buttons for all the heating zones and hot water. We also also fitted new tamperproof thermostats and frost stats to provide max/min temperature as well as new trv valves where required.

The result of the above has been a £7.5k saving on our yearly gas bill with an outlay of just under £1.5k (also replaced some old radiators and power flushed all 46 of them).

So thanks for all you comments, it certainly did help to steer the charity in the right direction without the expense of changing the boiler.

 

[Onetap]

Thanks for the offer, but we have now fitted one of these devices.

http://www.radiantcontrol.co.uk/pro...oiler-controls/boiler-controller-260e[/QUOTE]

AS with the BEM device it replaced,
IF fitted to a non-condensing boiler,
THEN the installation must include a means of maintaining the boiler return temperature above 56 degC (mixing valve, shunt pump, etc., ) or the boiler will be killed by corrosion within a year or two. It does not have a return temperature sensor (! ) .

This is mentioned in the manual is on P 10;
"For boilers that require a minimum temperature to
prevent condensation, set DIP (switch) 3 to Traditional Boiler."

And on P 12.

"Traditional Boiler
Traditional boilers are typically made of cast iron which
corrodes when exposed to the acidic condensed water
vapour. These boilers must operate at a minimum
temperature to prevent this condensing process from occurring. The minimum flow target equals 55°C - 1/2
differential when DIP 3 is set to Traditional Boiler."

I think that's wrong; the minimum return temperature (Tr) setpoint should be about 56 degC while the boiler is firing.

Even if it can keep Tr > 56 degC, the restriction will stop the weather compensation working effectively for much of the heating season. It is a boiler temperature reset controller and these are of limited effectiveness with non-condensing boilers. A system reset system works better but requires some major pipework amendments, e.g. a buffer vessel with a variable temperature mixing valve and pump set serving the distribution/secondary system.

 

[BEERMONSTER]

I agree these controllers are not as effective with a non condensing boiler and we have set the dip switch as such, but with the money we are now saving, we should be able to afford a condensing model in the future.

To defend the controller, the boiler cycles a lot less now and in summer it turns the heating off automatically for us. The hot water priority is also works well in our setup.

Given the age of the boiler, I was very surprised to see the savings we actually got while keeping the building comfortable.

Since the upgrades, we have also installed a unvented hot water cylinder which runs directly off our borehole. This is yet another vast improvement over the gravity fed systems. So we are moving forward slowly as money permits and I'm sure we'll get there in the end.

 

[Onetap]

I agree these controllers are not as effective with a non condensing boiler and we have set the dip switch as such, but with the money we are now saving, we should be able to afford a condensing model in the future.

......... the installation must include a means of maintaining the boiler return temperature above 56 degC (mixing valve, shunt pump, etc., ) or the boiler will be killed by corrosion within a year or two. It does not have a return temperature sensor (! ).

 

[BEERMONSTER]

I am fully aware it doesn't have a return sensor, but we have got a thermostat on the flow and return pipes so we can see what is going on.

Given the size/age of the building and number of radiators, the return takes a good few hours to get above 56C. This is the same with or without the 206e or BEM 4000 fitted! So it has run like this for 25+ years with no problems from corrosion on the heat exchanger. I fully understand that condensing can occur below 56C, but it has never caused any problems while the original BEM 4000 (also no return sensor) was fitted or now! The 206e has been in an working for over 12 months now and there was no sign of corrosion during its service last month.

So why over complicate things with fancy mixing valves and even more controls when the existing system has been proven over the last 25+ years continues to work well even with the new 206e unit.

I'm guessing that you (OneTap) don't like these units and hence slag them off in favour of more complex and more expensive systems. While I agree that there are systems that will work more efficiently, it is not always the case that everyone can afford to fit them. Its very easy to sit there and slag things off, but at 7.5k in savings and a boiler that is still operating fine after 25+ years of having this type of unit fitted, then your reasoning behind them being rubbish appears to be a little flawed. It may be different on a domestic boiler, but this isn't a domestic boiler!

 

[Onetap]

I'm guessing that you (OneTap) don't like these units and hence slag them off in favour of more complex and more expensive systems. While I agree that there are systems that will work more efficiently, it is not always the case that everyone can afford to fit them. Its very easy to sit there and slag things off, but at 7.5k in savings and a boiler that is still operating fine after 25+ years of having this type of unit fitted, then your reasoning behind them being rubbish appears to be a little flawed .

Unfair.
I did not say the Kanmor unit was rubbish, nor did I slag it off.
I think the bit in the manual that I flicked through (setpoint = Tf - 1/2 Tdiff?) is wrong.

I specified commercial control systems and IMHO have a better understanding of such control systems than most. I'm just giving you the benefit of what I know, free, gratis and for nothing. Leave it if you like or, if you know better, educate me.

I like cheap, cheap in installation costs and in running costs.

You have a 25 year old non-condensing boiler, probably a CI floor standing job. Kingfisher or summat. Fine; I had a non-condensing boiler until fairly recently and ran it with a buffer vessel & 3-port mixing valve. You could run the heating at low flow temperatures (say 35 degC flow) while running the boiler at 82 Tf 71 Tr. You couldn't stick the heating return from such a system straight into the boiler, it will rot it.

My sole involvement with the BEM thing was in a previous job, in which a manager had one fitted to an old, reliable floor standing boiler and later let everyone know how much it was saving. I said little because I then knew little about controls, but had heard some things about such boiler cycling controllers. That boiler was scrap within 6 months.

You (and he) changed the system.

So why over complicate things with fancy mixing valves and even more controls when the existing system has been proven over the last 25+ years continues to work well even with the new 206e unit.

Because it doesn't work without it.
You can't run your heating at 35 degC. You can't even run it at 55 degC Tf. Isn't that what weather compensation is supposed to do?

I'm not spending time on this, but I think the manufacturers have made assumptions about a constant temperature differential that may not be valid.

I am fully aware it doesn't have a return sensor, but we have got a thermostat on the flow and return pipes so we can see what is going on.

A thermostat is an on/off switching device.
If you have a thermometer on the return, I'd suggest that you check it doesn't stay below 55 degC for very long. If it's a clamp on job, I suggest you ensure there's heat transfer paste under the contact, the surrounding pipework is well insulated and that you distrust it.

I changed the non-condenser boiler for a condenser with boiler temperature reset weather compensation; no mixing valve. The old system was more comfortable.

If you'd worked out the savings for a new boiler and the manufacturer's control system, I think you'd have found the payback time justified the investment.

Cheap, see.

It may be different on a domestic boiler, but this isn't a domestic boiler!

I've done controls on 15 kW boilers and 3,500 kW boiler installations and most sizes inbetween. They are much the same, the control device isn't aware of the size of thing that it controls. You'd have more difficulty in justifying controls on the smaller jobs when they cost a larger percentage of the actual boiler installation costs.

 

[BEERMONSTER]

So from you last post you are saying that you would fit a more modern condensing boiler with a temperature reset unit which from earlier posts I understand the 260e to be.

The plan always has been to replace the boiler within the next few years once we can afford to do so. The recent mods put in place are to help us save the money in the short term and appear to be working very well. The short term goal was to restore the current system back to health without spending too much money which is what we did.

I am still unsure we will see any savings from a condensing boiler in the winter months as the current boiler has to work very hard to get the building to a comfortable temperature which is why we get a low return temperature for a few hours. During the summer months I'm sure there are definite savings to be seen.

Like I said, this is all work in progress and I'm sure we will get there eventually. I'm no expert in this area as I work in IT, but I do have an engineering degree which has given me some insight into each system and how they work. The better something is controlled, the more efficient it will be. But better controls often equal more expense. As with most things, it is a case of finding a happy medium that is acceptable to all parties.

The thermostats I mentioned are indeed thermometers (typo) and have been fitted with thermal paste and insulation to help get a more accurate temperature reading on the flow and return pipes. These were only added as a visual aid to help confirm the system is working as designed.

 

[Onetap]

So from you last post you are saying that you would fit a more modern condensing boiler with a temperature reset unit ................

I would probably have done as I said in my first post, modulating condensing boiler, or planned to achieve that eventually.

However, I don't want to pretend to be wise after the event; I didn't know how big the system was and that was an 'off the cuff' comment. You've installed the system that you thought best and no-one told you anything different.

I would do some 'back of fag packet' calculations, though with Excel since fag packets are a rarity now. Off the top of my head your existing boiler probably has an efficiency of 60% compared with say 90+% for a typical Vaillant or similar. Get the figures from the SEDBUK listings on-line. If you're now saving £7.5k per annum on your gas bill, I'd be fairly confident that your predicted gas savings would make a replacement look very sensible.

................which from earlier posts I understand the 260e to be.

You misunderstood.

The difference is that electronic controls have become much cheaper in the past 25 years.

A modern boiler would have a modulating burner so the output is variable from 25% or so to 100%. Instead of having a 50kW boiler running 50% of the time (under 50% load), you'd have a 50kW boiler running at 50% output 100% of the occupied time. It has frost protection built in, it needs no mixing valve. The manufacturer will have standard bolt-on controllers for weather compensation. It will tolerate low return temperatures.

I am still unsure we will see any savings from a condensing boiler in the winter months as the current boiler has to work very hard to get the building to a comfortable temperature
....................

You will, it's all in the 90% v 60% calculation of gas costs.
Whether those savings will pay for a new boiler is the main question.

I'd check whether the new controller has a facility to boost the flow temperature to the maximum until the indoor setpoint is reached. If the boiler flow temperature is set solely by the outside air temperature, it will take longer to achieve the indoor set-point.