Rate of increase in boiler flow temperature

[bw65587]

Well I think I have actually lost the will to live. I used to think it was just a phrase not an actual state of mind!

BG engineer came this morning. Both zone valves proved to be working satisfactorily, as did room stat and cylinder stat. However, he found the manual bypass valve closed even though the BG engineer who visited a week or so earlier said he'd left it a quarter turn open as it was closed. Is it me?

He thinks the programming part of the boiler is not working properly as the HW does not want to heat if its outside of a timed setting.

Anyway, opening the bypass seemed to stop the cycling...until it came on as normal at 16:00 this afternoon and the cycling started again!

So, a new circuit board being fitted to the boiler next week. Please someone give me strength!

Can I ask whether an automatic bypass would be better as the installation manual says automatic bypass valve?

 

[D_Hailsham]

Can I ask whether an automatic bypass would be better as the installation manual says automatic bypass valve?

Yes it would be better; a gate valve is just a compromise.

When the heating is on and all rads fully open there is no need for any flow through the bypass. But as rad TRVs close down, the flow rate through them decreases, so the bypass needs to open to provide additional flow through the boiler and maintain the required minimum flow.

 

[Agile]

Oops...

D Hailsham has forgotten to mention the most important need for the bypass which is to enable a flow path for the boiler pump overun flow to circulate round while the boiler heat exchanger cools down.

Since the heating and hot water will be timed as set independently then the boiler will always be timed for HW heating in accordance witht he timeclock settings. So I dont understand what the BG engineer means assuming that its not a combi boiler.

Tony

 

[bw65587]

Yes it would be better; a gate valve is just a compromise.

Will suggest to BG that they replace with one seeing as they were paid by me to sort it all out in mid 2009 and the regs stated then that an automatic one should be fitted where the manufacturer stipulates a bypass is needed.

There is another gate valve on the pipe that comes from the bottom of the HW cylinder. Should this be manual or automatic?

 

[bw65587]

I dont understand what the BG engineer means assuming that its not a combi boiler.

Sorry Tony. I think it's my poor explanation. According to the inbuilt programmer for the boiler, it should be possible to press the mode button and to just switch on the HW whenever you need the water heating, say in the middle of the day after the kids have had baths and used it all! The problem identified is that we can only get the cylinder to heat whilst the HW is actually timed to be on.

One thing I can see is that in the diagnostics menu, d.25 'Hot water activation via eBUS control' is set to 1 (yes). I'm not sure this is actually correct but it's a 'read only' setting so I can't change it.

 

[Agile]

Yes, you should see (and hear) the CH zone valve move. It's unusual for a valve to fail after a year, particularly Honeywell, so we nned tpo look elsewhere for the cause.

(Thought: did BG just assume the valve was a faulty or did they carry out proper diagnostic tests?)

That is NOT true on the Honeywell valves!

You can hear them faintly for 1-2 seconds as they open. You can hear them close as a short 1/2 sec whine.

BUT the lever does NOT move as they OPEN!

You can FEEL if they are open or closed though. If closed the lever only moves a few mm. If open the the lever will feel floppy and move freely for about 15 mm.

Some things are not mentioned in the text books!

Tony

 

[Agile]

Nowhere do I read of an eBus controller in any of your postings.

You also talk of the CH and HW both being controlled by timings that you set.

Until the BG engineer arrived you did not mention any problem about the boiler not following the timed settings.

I thought ( but could be wrong ) that eBus controllers are like "plug and play" so you just plug them and they override any other settings.

Tony

 

[doitall]

Yes it would be better; a gate valve is just a compromise.

Will suggest to BG that they replace with one seeing as they were paid by me to sort it all out in mid 2009 and the regs stated then that an automatic one should be fitted where the manufacturer stipulates a bypass is needed.

There is another gate valve on the pipe that comes from the bottom of the HW cylinder. Should this be manual or automatic?

It's also important to understand the above statement.

A gate valve is not acceptable as a by-pass valve, and hasn't been for quite some time.

 

[Agile]

Its only in the last few years when the benefits of TRVs in energy saving was promoted within the building regulations that auto bypass valves were required..

Before TRVs were commonplace the gate valve ( properly adjusted ) was reasonably adequate to achieve the required function.

The gate valve is approximately 15% of the cost of the auto valve and many installers take advantage of customer's lack of knowledge to just use gate valves. I class those installers as cowboys!

In your case fitting the correct auto bypass valve will enable it to conform to the currect regulations, it will not make a significant difference to your problems although every little helps.

The gate valve on your HW circuit is for a different purpose and is the correct type. Its for balancing the HW against the CH and helping to achieve the required flow/return differential.

Tony Glazier

 

[D_Hailsham]

Yes, you should see (and hear) the CH zone valve move.

That is NOT true on the Honeywell valves!

The lever does NOT move as they OPEN!

I know that, so I can't think why I said what I did. However I did not need to read a text book to find that out as I have a new Honeywell in my own installation and know from experience that you can hear the valve open and close.

As for the reason for having a bypass valve, I can't do better than quote Honeywell:

DU144 Automatic bypass valve can serve two functions:

a) As a boiler bypass as required by boiler manufacturers.

b) As a system bypass to accommodate pump overrun and to alleviate system noise that can be caused by increased pressures when thermostatic radiator valves or zone valves close down.

Which is more important will depend on the boiler and the system.

 

[bw65587]

BUT the lever does NOT move as they OPEN!

You can FEEL if they are open or closed though. If closed the lever only moves a few mm. If open the the lever will feel floppy and move freely for about 15 mm.

Quite true Tony, the lever doesn't move and the lever is 'loose' when the valve is open.

 

[bw65587]

Nowhere do I read of an eBus controller in any of your postings.

True. As part of trying to find the issue, we've now established that the HW will ONLY heat if the boiler is actually timed to do it. If we advance the HW on, it just doesn't work. The eBus reference is just something I've spotted in the diagnostics menu and wondered if this had anything to do with it.

 

[bw65587]

The more I learn from you guys and read about, I am beginning to think our pipework just isn't correct in the first place. We have no automatic bypass despite it being a requirement for the boiler and the regs but BG left a gate valve instead. It is also not placed before the zone valves as far as I understand but after them. Is this significant in any way as I read it should be before them?

 

[bw65587]

Untitled

• bw65587
• 22 Jan 2011
• 1

Current arrangement.

 

[OvertonPlumber]

muppets!

Since when do bG fit 38 hxis?
Surely its a BG330

Gotta love the magnaclean on the primary flow

Most problems on these boilers are caused by insufficient flow or contamination of the radial heat exchanger will can result in a whistling/trumpeting noise and kettling. The hex is very susceptible to crap as after all its only a 10mm stainless tube which is further constrained in certain points at the top of the coil.
Really the pumps need resiting on these systems much closer to the boiler as they struggle to pull on long flow and return runs either that or bung in a 25-65.