Length of 15mm pipe instead of an Auto Balancing Valve?

[jrldallas]

I have a Potterton Suprima 120 boiler and a Megaflow unvented hot water heater. I have been having problems recently with my hot water not working and boiler locking out (I know the Suprima does have a tendency to lock out but this is much worse than it was ever previously)

Looking at the pipework diagram for a Fully Pumped Sealed System, it shows an Automatic Balancing Valve between the Primary Flow and Return pipes, across the Cylinder.

On my system I have a short section (about 3 inches) of 15mm pipe running between the two 22mm Flow and Return pipes where a plumber told me there should be the Automatic Balancing Valve. I assume this is wrong?

The effect of this seems to be that the hot flow from the boiler is going through this "short cut" and "short circuiting" the Megaflow. I can tell this because the Return line below (towards the Megaflow) the 15mm short cut is cold, but above it (on its way back to the boiler) it is hot. The boiler is then cutting out because the return water is too hot, but the thermostat in the Megaflow is demanding more heat.

I am proposing to get the ABV inserted in the system and then the system power flushed (two plumbers have told me that the system is really clogged) as my theory is that the coil inside the Megaflow is clogged up which is causing the flow to short circuit.

Does this all make sense? Any other suggestions? Thanks for your help.

 

[bengasman]

Does this all make sense?

Not really; you are half right on some points and missing others. Chances are that there are at least 3 different issues here and possibly more.
Just find a good RGI, and let him get on with it.

 

[45yearsagasman]

As stated there are lots of issues that might cause your 120 to lockout.
Out of interest what pump is fitted to your system? Grundfos etc?
How was it established that your system is really clogged? How does the heating side perform?

 

[jrldallas]

Would have to have a look at the pump model when I get home.

I had some radiators replaced recently (which may have disturbed the system somewhat) and the water in them was really black. A later drain-down of the system also showed black water coming out which lead to the RGI recommeding a power flush.

 

[mickyg]

you seem to have had alot of plumbers round and no work done ! very odd! Please dont call me

 

[jrldallas]

Tell me about it mickyg. Hence why I am here trying to gather some opinions before I start shelling out again.

 

[Agile]

Tell me about it mickyg. Hence why I am here trying to gather some opinions before I start shelling out again.

You dont need opinions but rather definitive advice!

In your system black water is not much of a problem although of course its not ideal. Any helpful person changing rads would have drained the system a couple of times to get rid on most of the blackness and might have thought £20-£30 extra would have been reasonable for the extra time that might take. Perhaps you refused to let him? Or maybe he was chosen on the basis of price only and obviously the lower the price the less inclined to do any "extras"! I try my best to advise and do whatever is best for the customer!

Furthermore, what you have described would not normally cause the boiler to lock out but to merely turn off as having reached the set flow temperature.

You have not said if you still have the original PCB. There are few of these still in use! Most have locked out with increasing frequency and been changed when that was a few times daily.

Obviously you need the correct ABV to be fitted and for the system to be cleaned, probably just by simple flushing, and for an ABV to be fitted. But if its the old PCB that may just be demonstrating its impending failure!

Tony Glazier

 

[steve32]

Taken from manufacturers instructions

It is recommended that 35 mm pipework is used for the flow and return to within approximately 300 mm of the boiler.

The boiler requires a 22 mm by-pass for correct operation of the pump overrun. The total length of the by-pass circuit taken from the boiler connections should be greater than 4 metres. It is recommended that the by-pass circuit should be fitted with an automatic by-pass valve.

Circulation Pump Selection

The resistance through the heat exchanger when operating with a water flow rate producing an 11 °C temperature rise at maximum boiler output is shown in the table and graph in the mi's.

This is a high output boiler requiring a pump producing a high water flow rate. The system resistance including all control valves etc. must also be taken into account.

Most commonly used domestic circulating pumps do not produce the performance required, therefore a higher duty/ light commercial pump should be used.

To check for a blockage in pipework take a magnet and see if you have a magnetic attraction on all the pipework around the area of the cold feed, vent, pump and zone valves the stronger the magnetic attraction the more the pipes will be blocked
If there is an attraction then you will need to replace pipework on flow in area of cold feed/vent and system will need a good flush.

 

[Agile]

I think thats all too advanced for an average homeowner who expects to employ "plumbers" to do these kind of things!

Employing a plumber rather than a boiler engineer is a bit like expecting your GP to know as much as a cardiovascular consultant about an aneurysm!

Tony

 

[steve32]

I think thats all too advanced for an average homeowner who expects to employ "plumbers" to do these kind of things!

The op needs an installer/repair engineer not a "plumber" used to the 120/120L.
This beast is not the same a 30-100 suprima.

Steve

 

[Agile]

Exactly!

 

[DP]

OP try resetting the ABV according to the instructions. May just be a case of balancing valve not closing to allow circulation through the megaflow

 

[bengasman]

Tell me about it mickyg. Hence why I am here trying to gather some opinions before I start shelling out again.

What are you trying to achieve with those opnions?
Who cares what 15 of us think it might be? (unless you want to try and diy the problem, which is probebly a bad idea )

 

[steve32]

OP try resetting the ABV according to the instructions. May just be a case of balancing valve not closing to allow circulation through the megaflow

According to the OP there is no ABV fitted on the system just a 15mm by pass

 

[jrldallas]

Don't worry bengasman I'm not going to DIY it. I just want to have some ideas so that when I get someone round I can have an "educated" discussion with them. I don't claim to know anything about heating systems, but I trained as an electrical engineer so am happy to learn a bit.


re the pump. It is a Grundfos and UPS 15-50 130. If so, is it suitable? Has been in the house for at least 5 years but that doesn't mean it is the right thing for the job!