Boiler ramping up then cutting out - no circulation

DazzaMazza

Hi,
I need some advice on a boiler issue. During the summer I had a rad changed in the house while we were doing some renovating. It replaced an old rad that we could no longer bleed etc.
At the end of the summer I fired up the boiler only to discover that it would ramp up to about 75 degrees and then shut off, drop down to 32/33 and then begin the cycle again. I thought it might be a dodgy zone valve so I had a local plumber replace the two zones valves (which as it turns out needed replacing anyway. No joy, same issue. The boiler company came to service, said the boiler was fine and it was a circulation issue and therefore my issue. I was doubtful about this, nothing in the system had changed bar the new rad being added. Granted it might have caused some sludge to move or cause a blockage?

The builder who changed the rad came out, took a look and then paid a plumber to take a look (hes a guy I'd trust). He was happy that the rad change didn't cause the issue. He tried flushing a few rads with a hose but no change. He recommended a power flush in case something had shifted and caused a block or the system had sludged. He did comment that the water was not clean and the company who installed the boiler should have flushed the system originally (which they did not)

SO....plumber comes back, does a powerflush, takes about 8 hours to wash it out, adds inhibitor etc. Used Fernox. He's happy that the circulation is fine. The washer pumped water through the boiler for 8 hours, reversed the flow a few times, flushed each rad etc. The rads were hopping off the walls with heat about 10 minutes after the flush began and the boiler held the temp for the 8 hours while being flushed.

After the flush, he put the boiler bpump back on and its the same story. No circulation and little heat. Rads will heat but it takes a few hours. He reckons its either the system pump which sounds ok or a blocked heat exchange which is blocked enough for the system pump to struggle with.

Anybody experience something like this? Any advice welcome. I have a yearly warranty and I will be contacting the company but I'd love some advice as its going on too long.

Thanks

Dazza

K.Flyer

The last guys opinion is probably nearer the mark.
Partially blocked heat exchanger or a weak circulation pump.
If it took 8 hours to clean out the system, I would think its most likely both items are in need of replacing.

DazzaMazza

Thanks! Reason for 8 hours is that there are 15 rads so it took him a while and also he wanted to leave the chemical circulate for few hours at the start. Appreciate the response

Dtp1979

DazzaMazza wrote: »

Thanks! Reason for 8 hours is that there are 15 rads so it took him a while and also he wanted to leave the chemical circulate for few hours at the start. Appreciate the response

What boiler do you have? It could be a blocked filter in the boiler, the automatic bypass in it could be stuck open in it either, therefore the circulation would only mostly occur in the boiler and not the system. My bet is on a filter though

DazzaMazza

Its a bosch. Only serviced a few weeks back though and they blamed a circulation issue, which Im now 99% certain that its not given the flush managed to flow around the system without an issue and the house was 25c after 30 minutes!

Dtp1979

DazzaMazza wrote: »

Its a bosch. Only serviced a few weeks back though and they blamed a circulation issue, which Im not 99% certain that its not

Did they check filters

Egass13

DazzaMazza wrote: »

Its a bosch. Only serviced a few weeks back though and they blamed a circulation issue, which Im not 99% certain that its not

Which model is it ?

DazzaMazza

Its a greenstar 30 cdi. Not sure if they checked filters, assume they might have during a standard service

DazzaMazza

Just to complete this thread, turns out it was the pump
Really annoyed at the time, company insisted it was the system, when it flushed and we proved that circulation was fine, they admitted a pump failure. It sounded ok but you could stop it with your finger. Needless to say I've dropped the company involved from servicing it in future.

DazzaMazza

DazzaMazza wrote: »

Just to complete this thread, turns out it was the pump
Really annoyed at the time, company insisted it was the system, when it flushed and we proved that circulation was fine, they admitted a pump failure. It sounded ok but you could stop it with your finger. Needless to say I've dropped the company involved from servicing it in future.

In truth I'd say ye are both right as your defective pump is probably a symptom of your contaminated system water.