worcester 400 electronic CH cutting out

[smagsmith]

Hi All,


I am looking for some advise on the problems I am having with my boiler. It is a Worcester 400 electronic series. It was new in 2003. Generally it has been great, but this last six months have been a pig. Problems started when we put the heating on back in October.

DHW was cold and so was CH in certain radiator. Upstairs radiator worked fine, but downstairs got no heat at all. Engineer diagnosed a circulation issue and probable sludged heat exchange plate.

I spent a couple of months working on circulate by draining and using cleaning chemicals. Each time the drained water got cleaner and cleaner, it started off pitch black like ink, but now looks like a light brown colour. I think I have drained and used fresh chemicalls 6 times now (two weeks of running each time before emptying). DHW improved straight away.

Finally got some break through with downstairs rads. They get some warmth, but not great. I have rebalanced the system which has helped. I have noticed that if I drain via the fitted drain valve (Flow loop)then the system can drain in 10 min. It I connect to the return flow then it takes 40 mins. I think the return still has circulation issues, but it is better than it used to be.


Hot water has improved massively, but still get a slight flux in temp, but no where near what it used to do. Biggest variance is noticed when on full flow running a bath.


Biggest concern I have is the CH. The boiler seems to cut out and stop producing CH hot water. I can feel the pipe get really hot coming out of the boiler, but it only last for 30 seconds, then the boiler cuts out and the pipe cools down. The cut out lasts about 3-4 mins then the boiler fires up again, the flow pipe heats up, then it cuts out again and the pipe goes cold.
I am getting no sustained flow of hot water into the rads. There are no flashing lights that I have seen before when the system reaches low pressure. Does anyone know what is causing this cutting out issue?
Engineer has been back out and is suggesting replacing the heat exchanger to fix the DHW temp variances, but will that also fix the CH issue. I am nervous about paying for a new exchanger plate if the circulation is still not right and I end up sending contaminated/sludged water into the new exchanger plate.



Any advise much appreciated.


Cheers
Steve

 

[chris watkins]

Hi Steve & welcome
It is poor flow through the boiler that is not allowing the heat produced to be carried away so the boiler stops firing until it cools. Changing the plate for the hot water production will not alter this if the heating side is bad.

The trick is to try to find out where the restriction is located, is it the boiler main heat exchanger or the heating system (after checking the pump out first).

As you have found out you are unlikely to shift hardened oxides with chemical cleaners (& even a power flush may not do it)

 

[smagsmith]

Hi Steve & welcome

The trick is to try to find out where the restriction is located, is it the boiler main heat exchanger or the heating system (after checking the pump out first).

Thanks for the reply Chris. How do I find where the restriction is? I am a complete novice who has been on a steep learning curve. A few months ago all i could do was bleed a rad. Now I can drain and stsyem and add cleaning chems and take off a rad to flush in the garden with a hose pipe.
The pump was replaced last month as part of the maintenance deal I have.

I believe that the general circulation round the rad loops was the initial problem, but think that has got better as rads that periously did not work , now do. But they are nowhere near what they used to be a year ago. How can I test if the restriction is back to normal round the rads? Is there a way to measure the flow when draining down? I get good drain speed from the flow, but pour drain speed from the return (draining from flow and return on same rad)
When you say 'boiler main heat exchanger or heating system' what exactly are you asking me (Sorry for newbie question)?

I have read on other threads that the diverter valve can cause similar problems.
I can get my head round the fact that if the boiler heats up water ready to pump round the rads, then if that water cannot flow then it will remain in the boiler and overheat. What I can't work out is why the water is struggling to flow round the system? What is stopping it? Is it a boiler issue (not the pump unless the new one is faulty) or is it a circulation issue somewhere in the pipes/rads. Does the poor drain speed on the return loop indicate poor pipe circulation and if so could this be causing the overheat in the boiler? Any tips on how to locate the problem?

Cheers
Steve

 

[Millsy 82]

I think you need a gas engineer to have a look at your boiler.

 

[chris watkins]

As above,
All I can tell you is that there is a restriction some where around the circuit (rads & boiler) & this is not allowing enough flow, most likely from all that sludge / deposits that you have liberated with all your flushing & chemicals. These have got caught up somewhere where the pipes narrow, now it could be the pipework circuit out to the rads or it could be around the boiler.

All you can do is maybe connect the flow & return together so that you know that this is clear & free with a good flow. If the boiler still does not fire for very long before it cuts out then the boiler is your problem. Then you would have to get an Gas Safe heating Engineer to take a look.

You will not get any further help on this forum as by Law & for your own safety you cannot work on it.

You do understand I hope Steve

 

[Rickster123]

Great advice given. Thread closed.