Gas boiler, controls and prog/stat

[Cliff Topp]

What is the relationship between the controls on the boiler itself, the thermostat/programmer in the hallway and the heat in the rooms?

Our previous boiler was an Alpha CD32C and the boiler controls for both heating and hot water were numbered from 0 to 9, and both were set to No. 7. The thermostat/programmer in the hallway was only rarely set to above 18C. Only on the very coldest days of winter would we have to put it up to about 20 or 21C.

Our new boiler is a Worcester Greenstar 30i and instead of the boiler controls being numbered 0 to 9, the readout is in actual degrees Celcius. Both heating and HW are set to 56C but I don't know if that was set at the factory or if the installers set it.

We are finding that 18C on the old stat/programmer in the hallway was more than comfortable for us but the new stat/prog has to be set to at least 20C or 21C to 'feel' as warm as it was before.

I don't know what the *actual* temp of the rooms is as we don't have a standalone thermometer, but it's weird trying to get used to this new system.

On top of that, and perhaps even more importantly, is the frostat.

The old Alpha boiler was up in the loft for 14 years and as far as I know it never had a frostat connected - unless it was factory-fitted and integral to the boiler itself but definitely no external unit was wired in.

The new installation *does* have a (Honeywell) frostat wired in and it's keeping the heating on all night, irrespective of if I turn the hallway stat/programmer down to a very low level or completely off. This is really bad in three ways:

1. Extra gas used equals bigger bills
2. Even though the rads are only lukewarm to the touch, we aren't used to *any* form of heating on at night and it's making it difficult to sleep
3. The pipes and rads creak and groan a lot which is making it almost impossible to sleep!

Any advice?

[charles]

Change the setting on the froststat so that it comes on at a lower temperature.

I'm not sure if your pont 1 is true, The boiler doesn't need to work so hard first thing in the morning if the house is moderately warm when it is told to heat the house.

[Tricky Dicky]

We had Bosch Greenstar I think 35i in the garage at the last house it had a frost stat connected due to risk of freezing. Ideally they should be set at 7C but you can go lower say 5/4C below that there is serious risk of freezing. The draw back using a frost stat is that it works independently of the the room stat so with a single heating circuit you will get radiators heating up at night if it kicks in. It should not have a major impact on gas usage. The extra cost of fuel has to be weighed against the potential damage caused by freezing.

As for comfort level differences it might be if you had an old mechanical room stat it?s settings may have been inaccurate, modern electronic versions tend to be much more accurate.

Richard

[bert]

We have Y plan system (I think) CH and HW are controlled independently by motorised valves which turn on boiler/pump as required independently of each other.

The boiler (Worcester Bosch) has a built in frost stat, but if that activates the pump will only run on the bypass overrun circuit. It cannot open the motorised valves to put the heating on. They are controlled by the thermostats, one in hall for CH and done on tank for HW always assuming the specific timer is ON. But our system is over 10 years old. Maybe progress has struck again.

[Alan]

Different thermostat, different mean temperatures, that isnt unusual.

It sounds like it has been wired wrongly, and the frost stat is calling for heat by opening the CH valve. It may be something to do with the plumbing pipes too, there should be bypass piping to allow the boiler to run without having the CH valve open. You clearly know nothing about it, and it sounds like your fitter didnt either, so probably time to get someone in who knows what they are doing.

[Roger Mills]

More likely to be an S-Plan if there are separate motorised valves for each zone and a by-pass valve. Y-Plan systems use a single 3-port valve, and don't normally need a by-pass.

But if you *only* run the boiler and don't heat the rads, they and the pipework could freeze up. You wouldn't want that, surely?!

[Tricky Dicky]

Agreed Roger our frost stat was a separate unit not part of the boiler and controlled the CH valve just as the room stat hence the radiators getting lukewarm but unlike the room stat it was not wired through the programmer being solely triggered by the temperature falling into its set range.

Richard

[John Rumm]

On a traditional setup, the stat on the boiler will set the upper limit on the flow temperature of the hot water produced by the boiler. With old fixed output boilers that basically means it runs flat out until the primary water exceeds that temp, and then cuts power to the burner (while still running the pump) until the temp falls.

With more modern modulating output boilers, they will aim to set the flow temp to that limit by adjusting power to match the actual load. If the load is too small that its unable to modulate lower, then they revert to the style of operation used by fixed output boilers.

In a perfect world, the stat in the hall ought to keep the place feeling the same regardless of how cold it is - it would just run the heating more frequently to compensate for the higher rate of heat loss. However as you have discovered, that does not always work of the boiler can't heat the place fast enough on cold days.

(this is where weather compensation systems can be used to ramp up the flow temperature on the boiler in sympathy with the external temperature)

Probably set by the installers. Also probably a bit on the low side on cold days unless you have oversized radiators.

(54 degrees is the *return* temp at which you get a notable improvement in condensing efficiency for the boiler)

You will probably need to set the temp for the rads on the boiler a bit higher during the colder parts of the year. 56 will be fine for the "part load" months.

See 5.8 (7):

"7.Explain to the User that an internal frost thermostat is fitted in the boiler, and that the electrical supply to the boiler must be left on for the thermostat to operate"

Well firstly a frost stat *should* override any others - its there as a failsafe. However the greenstar also has an internal frost stat:

It might be that the installers were worried that the pipework in the loft would cool faster than the boiler - but that seems unlikely since the boilers one kicks in a 8 degrees.

ISTM that the external stat has been wired incorrectly or set at too high a temperature. Since the boiler has its own internal stat, I would be tempted to simply disconnect the "call for heat" from the frost stat and see how that works.

[ARW]

A properly wired frost stat should be wired in series with a pipe stat.

[Fredxx]

Don't you mean in parallel? A pipe-stat is a very 'local' temperature measurement and would turn off the boiler virtually as soon as it fired up?

[Andrew]

If that is likely then maybe you need to think carefully at how good (or bad) your house is insulated.

[Cliff Topp]

Thanks John, very helpful. I'll have a look at those links now.

[ARW]

No. In series.

The pipe stat is supposed to be on the return pipe to the boiler at say

20 deg.

[Roger Hayter]

As a matter of interest, what is that supposed to achieve? And does it exclude the possibility of pipes in the loft freezing while the boiler is still cooling towards freezing?

[Roger Mills]

Unless the boiler is in an unheated outhouse or attic, why would that be any more likely to freeze than the pipes?

[Dave Liquorice]

temperature

Well you're only worried about the heat exchanger or pipe work freezing. You're not overly worried about the loft/garage being maintained at 7 C or WHY. Once the boiler has fired long enough to raise the return to 20 C you don't need to run the boiler any longer. I think I'd be happier with that return temp to be above the likely maximum house temp though, so heat from the house doesn't turn off the frost protection. Say 30 C.

Indeed one might get satisfactory frost protection by just running the CH pump with the CH valve open. Would only work if the heating was on, so the house was warm, and maintained warm, even if set back.

[Dave Liquorice]

Boiler has balanced flue that could allow cold external air to circulate through the heat exchnager.

[Dave Plowman (News]

56C is likely well below the temperature the old boiler ran at. Meaning the rads might well struggle to heat the house. So just what a room stat says may not be achievable.

[Cliff Topp]

Just FYI if anyone is interested you can see photos of the setup here:

or if that wraps incorrectly

[Tricky Dicky]

Richard