Condensing Boiler Cycling

[Skid Solo]

Hi

I am not sure if I have an issue or not but would like some help, 1st the history

I had a new heating system installed this summer in to a 5 bedroom 3 bathroom house:
• Valiant Eco Tec 637
• 22 New Radiators (Stelrad)
• Un vented hot water system (Glow Worm cylinder)

The pipe work was also upgraded as it was 8mm microbore so house was zoned upstairs/downstairs/hot water, with 22m from the boiler for each zone down to 15mm for the rads. All rads have TRV’s Drayton TRV4’s fitted except for the two upstairs and downstairs hallways near the room stats.

The radiators were specified by myself and the 1st engineer I wanted to do the job, he agreed the size of each rad based upon the room size and the value of all rads came to 22KW, a 37KW boiler was selected to allow for the hot water system and some scope for future expansion. I purchased all the radiators (I was quite happy to install all the radiators and he was happy to just connect to were I had installed but we had to agree that they were the correct size)

Anyway the 1st engineer let me down, don’t know why but it wasn’t just me he let down, so I found a 2nd engineer. Again he was happy for me to install all rads and he would just connect. When he installed all the new pipes

Everything appears to working fine and the house is so much hotter than it was last year where the old system was on 24 hours a day 7 days a week over the really cold period. The old boiler was over 30 years old, leaking and had not been upsized when the house was extended so had to go.

Anyway being new to Condensing boilers and having read this thread I wonder if 637 should be cycling as it does, this is what happens :

• The boiler starts, the pump starts and the gas burner symbol comes on until the temperature reaches 75. This normally takes around 1 mintue15 seconds
• The gas symbol burner then goes out and the pump continue to run until the temperate drops to 49 which normally takes around 3 minutes 15 seconds
• The pump then switches of for around 10 seconds
• The pump then switches back on for around 10 seconds until the burner starts and the cycle starts again

Is this correct for a condensing boiler ? or am I damaging the boiler or not operating it efficiently

I have spoken to the Engineer who installed the boiler and he has told me to keep an eye on it (not sure what that is going to do) his statement is that as I specified the radiators so are they the rights size for the rooms. They were according to the 1st engineer and with all the information I have found. So he hasn’t washed his hands of this entirely but doesn’t seem keen to come back and check it out. So I want to understand if the boiler should be operating like this or I need to push the point

Thanks

 

[Agile]

You seem to have had a nupty first engineer who did not know that you only allow 2 kW for water heating assuming that you dont expect to nearly double your house size to use up the remaining 15 kW.

Then you had a second nupty engineer who did not set the boiler heat output to better match the needs. So your boiler pumps out 37 kW and reaches the 75 degrees set quickly and turns off on the anticycling delays for three minutes during which it gives out no heat at all.

You can set the maximum power output yourself to about 24kW if you are good with computer type settings. See the book.

But the installer should have done that himself. Presumably he did not complete the Benchmark Certificate or inform Building Control or advise the manufacturers of the installation to start the warrantee period?

Tony

 

[Skid Solo]

1st engineer based the boiler size on 6kw for hot water.

2nd based upon whole house size

As they came out the same I did not question.

2nd engineer did complete Benchmark log book (although he did not complete ‘Central Heating Mode’ section, should he have done that ?) and notify warrantee period, not sure about building control

Would however he have been able to commission properly as it was installed in the height of summer

Will have a look at turning down, but think I attempt to get 2nd engineer back, I paid him enough to install it.

 

[ajrobb]

Even if the boiler is too big, cold radiators should supply sufficient load to keep it running several minutes. I doubt the radiators are all hot within 75 seconds.

The manual states there is an internal automatic by-pass and the factory setting is 0.25 bar. It has a range of 0.17-0.35 bar. If it was me, I'd have a bash at re-balancing the radiators to reduce short circuits and/or increase the flow through the boiler. If that didn't work then I'd want to try cranking up the by-pass pressure...

 

[cozzmic]

Glowworm UVHWC rated at 19 to 26KW coils.

 

[ianniann]

Agreed this is pointlessly over-sized but does the 637 not modulate itself down?

 

[Boilerman2]

If the Heat input is not correctly restricted the boiler will produce 37Kw which will cause the water to reach its upper control temperature the burner will be unable to modulate down quickly enough to avoid overshoot this will result in a three minuite shut down "anti cycling procedure" by which time the boiler is cold again so the whole cycle starts again! as Agile has said set otion "d 0" to approx 24 (24Kw) this will resolve the issue and enable the boiler to fire for longer periods of time which will much more economic!!

 

[Razor900]

Is the pipework 28mm from the boiler reducing down to 22mm for each zone valve or is it all 22mm

 

[Skid Solo]

Yes its 28mm from boiler to each zone and then reduces to 22mm