Honeywell Y Plan Not sure if working correctly

[dormermike]

Hi

Just a couple of questions, hope nobody minds as they may be a bit noddy i guess. System is a open vented Y plan system, CM927 wireless stat, Ideal Mexico Super 2 boiler (36kw), 14 rads. Stat is in living room which has the TRV removed. All other rads apart from the boiler circuit rad have TRV's.

I have read the FAQ on the 3 port valve too, but I am still confused - if I move the lever, should it start the boiler? Mine doesn't - not sure if thats a fault or correct operation?

When the heating is "on" (via CM927) the boiler occasionally fires only for very short bursts..some times as short as 3-5 seconds - the flame symbol would be showing, and the target temp is higher than the actual temp (often by a few degrees) so trying to heat the room. This is usually first thing in the morning for example, when house is coldest. When this happens, the CH pump is running, or is by the time i get upstairs to check.

Could it be that the CM927 is calling for heat, and powering the pump, but the boiler is "satisfied" by the boiler stat (which is turned to 4 out of 6)?

The system operates pretty well and keeps a consistent temp, im just concerned that the boiler firing for such a short period is adding wear and tear and is wasting gas (it cant possibly be heating anything can it, in such a short period?).

Any opinions very much appreciated.

Thanks!!

EDIT: CM927 is configured to factory setting.
EDIT2: Had a RGI around recently to service it though he talked me out of having the chamber dismantled and swept. Gas readings all normal. He said boiler was working fine, to keep it and just forget about it. Took the mick a bit that i was bothering to get it serviced, said it didn't need an annual service.

 

[dormermike]

Nobody ?

 

[swbjackson]

36Kw is a big old boiler. Could easily be oversized for the system, particularly if TRVs are shutting down so the heat isn't getting away from it very quickly.

 

[dormermike]

thanks - i guess speeding up the pump might help if that was it - though the pipes dont feel particularly hot. Its something to consider anyay, i'll investigate.

Also if I move the lever, should it start the boiler?

 

[dormermike]

Can anyone confirm if, on a Y plan, moving the lever on the 3-port will fire the boiler under any circumstance please (eg DHW on, CH on, or either one or both off).

Or are the microswitches solely for the purpose of feeding back actual position to the rest of the system?

Thanks - have read the FAQ but it is not clear on this point.

Cheers

 

[mysteryman]

No. It doesn't move the valve far enough to operate the microswitches. It is there for system filling and venting, or to give temporary central heating if the Synchron motor fails. The hot water controls need to be calling the boiler on for that to happen.

 

[dormermike]

No. It doesn't move the valve far enough to operate the microswitches. It is there for system filling and venting, or to give temporary central heating if the Synchron motor fails. The hot water controls need to be calling the boiler on for that to happen.

Excellent - thank you. Just what I was looking for.

Cheers

 

[D_Hailsham]

Ideal Mexico Super 2 boiler (36kw), 14 rads.

Can you confirm the model? The GC number (on the data plate) is best.

Could it be that the CM927 is calling for heat, and powering the pump, but the boiler is "satisfied" by the boiler stat (which is turned to 4 out of 6)?

That's a possibility. Turn the boiler stat to 6 and see what happens.

The CM927 has a minimum on time of one minute, but a motorized valve can take up to 30 seconds to move from HW to CH. However a mid position valve stays in the CH only position when CH is satisfied, so you only get this problem when moving from mid-position to CH only.

Why do you have a 36kW boiler for 14 rads, which probably don't add up to much more than 28kW?

 

[dormermike]

Thanks

If i turn the boiler stat to 6 it kettles - or it did when i last tried it. 5 works ok, but it still shows the behaviour i described above.

Model is RS125, GC number is 41-621-07

The boiler was here when i moved in. I guess because there are some large double rads (x2 in conservatory of 3 metre length) and a 2800x800 double double in the living room and its a pretty big bungalow overall.

All the pipe work is 22mm down to 15mm for the long runs then varying lengths of 10mm to the rads, so all rad tails are 10mm, even to the monster rad in the living room. The RGI said that would not get it fully hot as 10mm is not sufficient for that sized rad, but it gets stinking hot in there so i dread to think what 15mm tails would do!

EDIT: Kettles after a while (>30 minutes of running) when set at 6 (max)

 

[dcawkwell]

Poor circulation.
Pump or a blockage.

 

[D_Hailsham]

The RGI said that would not get it fully hot as 10mm is not sufficient for that sized rad, but it gets stinking hot in there so i dread to think what 15mm tails would do

Is there a noticeable difference in temperature between the two pipes of this radiator? (You can tell by feeling the pipes.)

 

[twgas]

I'd be suggesting a new boiler, you got a very inefficient boier that is quite possibly twice the size it needs to be and you're worried about a few seconds of running it and think it wastes gas.

 

[dormermike]

The RGI said that would not get it fully hot as 10mm is not sufficient for that sized rad, but it gets stinking hot in there so i dread to think what 15mm tails would do

Is there a noticeable difference in temperature between the two pipes of this radiator? (You can tell by feeling the pipes.)

Yes, i would say so. I have throttled it back on the lockshield, so it is not fully open.

 

[dormermike]

I'd be suggesting a new boiler, you got a very inefficient boier that is quite possibly twice the size it needs to be and you're worried about a few seconds of running it and think it wastes gas.

Thanks, but i think spending 2k on a new boiler would not be of interest. Costs dont stack up for me, and this boiler would probably have more life left in it than most boilers currently waiting to be installed

i just want to make sure the whole system is working as best it can.


Cheers

 

[D_Hailsham]

Model is RS125, GC number is 41-621-07

Can't find a manual for that GC number. It must either be very old or could you have written it down wrongly.? Who is the manufacturer as show on the data plate?

Other versions of the Mexico RS125 have an output which can be adjusted between 30kW and 36KW. That is a very high output, unless the house is extremely large or has poor insulation.

Unfortunately installers tended to put in very large boilers to make sure that the customer couldn't complain that the house was too cold. That was OK when gas was cheap and "The Gas Board" had a monopoly.

You can find out what size boiler you really need by using the Whole House Boiler Size Calculator. You may get a surprise.