Boiler not firing constantly when heating up from cold

[evets51]

Hi, I've got an Intergas system boiler on a system with mini-bore piping. Had quite a lot of trouble as when it was first installed 1.5 years ago, the powerflush done at installation time didn't work (was done from one of the radiator pipes which being mini-bore didn't allow for enough pressure). Result was the house never got hot, had two further engineers out and then the system re-flushed by someone who specialises in mini-bore flushing and did it off the main pipe out of the boiler. At the end of the process they showed me the sludge removed and demonstrated the flow that was now being achieved - they also guaranteed their work and offered to do a second flush for free if anyone could find any blockages in the system, so I'm happy it was done correctly this time.

The house now gets hot as do all the radiators - problem is it takes almost an hour for the radiators to get to full temp. All 3 engineers I've had out have said there seems to be something funny with the boiler in that when heating the system up from cold, it doesn't fire constantly - it will fire for a minute or two then cut out for another minute or two. It still does this now.

Intergas no longer have an agent in my area and are going to have to send someone in from a fair distance away. Over the phone they've told me that the boiler is designed to do this so that it can maintain a 20 degree differential between flow and return to aid the condensing process. They recommended that I turn the power down and try that (its set to maximum usually) - I turned it down to 65% as recommended and this made no difference. Their argument seems to be that if the return flow is more than 20 degrees cooler than the out flow, the boiler will stop firing to remain efficient. That's all well and good when the radiators are hot, but surely seems wrong if it means its taking an hour to get my radiators hot? Or is this just something I have to live with?

 

[jam1979]

IT COULD BE A NUMBER OF THINGS CAUSED BY SLUDGE I E blocked heat exchanger pump not taking the heat away fast enough due to sediment in it the plumber should have flushed it for twice as long as on a normal flush if its a 10mm micrabore if its 8mm I doubt if hes even flushed it he may just have added some inhibiter

 

[dancinplumba]

Poor flow, heatex on boiler will not be blocked, its an Intergas. How did you reduce output to 65℅ ?

 

[jam1979]

ive just read up on them intergas boilers they seem to very good

 

[dancinplumba]

They are

 

[evets51]

IT COULD BE A NUMBER OF THINGS CAUSED BY SLUDGE I E blocked heat exchanger pump not taking the heat away fast enough due to sediment in it the plumber should have flushed it for twice as long as on a normal flush if its a 10mm micrabore if its 8mm I doubt if hes even flushed it he may just have added some inhibiter

Its 10mm - he was here flushing for over 10 hours, I watched him cut into the pipe that comes out of the boiler, connect his machine up and watched the pump running / saw the sludge being removed. Previous to this I had had X400 System Restorer in there for a month which had made a big difference in itself.

The problem is that the output pipe from the boiler is getting too hot relative to the return pipe - you can feel the big difference - so the boiler cuts back to keep that differential balanced. So I think the heat is getting from boiler into the water just fine. Its a big-ish system - 17 radiators - so my guess would be that it has a lot of water to heat up / pump around, which is why the return is a lot cooler than the flow for a while - but surely then it should work at full crack until its all hot rather than cut out?

I cut the power back by using the electronic control panel on the front of the boiler - there are instructions in the user manual for doing this and the tech guy from Intergas talked me through it. His reasoning was that if the output was too hot, cutting back the power would warm that output up more slowly and thus the boiler would work constantly rather than cutting out. Didn't really make sense to me ... and like I said I tried that for a week and it was still cutting out and taking even longer to heat up, so I set it back to full power.

 

[chris watkins]

Not enough flow rate through the boiler, What model have you got installed 18, 24,30 or 40 ? (17 rads)
Do you know what size the main pipework is to & from the boiler ?
Was an automatic by-pass installed when the boiler was installed ?

 

[evets51]

Not enough flow rate through the boiler, What model have you got installed 18, 24,30 or 40 ? (17 rads)
Do you know what size the main pipework is to & from the boiler ?

Its an 18 - I've had a radiator output calculation done by an engineer and its big enough, just. 22mm pipes to / from the boiler, splits into 10mm further down the system.

 

[jam1979]

has it got 10mm pipes tapping off the 22mm flow and return so there is 22mm straight 2 and from the boiler

 

[chris watkins]

I thought you were going to say you had a 30 or a 40. Sorry I edited my first post - was an auto by-pass installed when the boiler was installed (MI sate at least 20ft away).
Last off do you know what the pump speed is set to (should be 3) even then it may not be enough to overcome system & boiler resistant's as it max head is less than 4.5M.
Do you heat your domestic hot water off the boiler as well, if so try having both heating at the same time & see what boiler does then ??

 

[evets51]

I thought you were going to say you had a 30 or a 40. Sorry I edited my first post - was an auto by-pass installed when the boiler was installed (MI sate at least 20ft away).
Last off do you know what the pump speed is set to (should be 3) even then it may not be enough to overcome system & boiler resistant's as it max head is less than 4.5M.
Do you heat your domestic hot water off the boiler as well, if so try having both heating at the same time & see what boiler does then ??

Yeah I thought I would have needed a 30 but the one that was in before was only 16.5 and worked fine, and the calcs were done to come up with 18 based on radiator size ..

The pump is on 3 and yes there is a bypass (it was there from the previous system) - towel radiator in a bathroom at opposite end of the house to the boiler. The system does do the hot water also (via a storage tank in the airing cupboard) and runs continuously if both hw and ch are on at the same time.

So if the pump in the boiler isn't man enough for the job are there any alternatives i.e. a secondary pump? I have a Monsoon 3.0 bar twin pump for the hot water next to the storage tank in the airing cupboard because the hot water pressure out of the tank wasn't high enough without it, could I have something like that for ch too?

 

[chris watkins]

Towel rail as by-pass will not be enough, I am guessing. If boiler runs fine when heating both hot water & heating then it is the flow rate around the heating alone, who install this ? seems they didn't really know what they were doing.
Low loss header & new pump to handle the high resistant's heating. (yes but not a monsoon LOL) not a diy job I am afraid.

 

[Ollieg]

Sounds like there is too much resistance across the heating system. Or you have a failing pump.