Frost stat help!!!!

What Baxi.

 

looking at these instructions the typical frost stat should fire up the boiler, however not sure for how long, the normal central heating controls open and close motorised valves and once the valve is open then the valve fires up the boiler as the micro switch in the valve is activated. The diagram shows the frost stat by-passing the valves so they would not open. However all the valves and thermostats are external to boiler, so we have no way of knowing how it is wired, we do have standard honeywell plans Y, S, W etc, but we don't know which, and if people on site can't sort it, not much chance sorting it using a forum.

 

The frost stat is a simple on or off, so if it powers the pump then it must also power the boiler, today with programmable thermostats there is no need for a frost stat, there were used when the programmer and the thermostat were separate items, so if the programmer was off the frost stat still works the central heating. Only problem is if the programmable thermostat uses batteries then if they go flat no frost protection, I change mine every year be it needed or not for that reason.

In this diagram the pump and boiler are connected together so should be impossible to run pump without the boiler, however the orange wire does not operated the motorised valve, 5 or 7 needs to be powered on the valve for it to open, 8 is a supply from the valve not to it, so unless there is a by-pass valve then water could not flow, most boilers either have a pressure sensor, flow sensor, or over temperature sensor which would either stop it firing up or cause it to fire up then close down again.

The wiring shown in the manual I have linked to does not seem to make sense. I would wire the frost stat in my wiring diagram from line to brown/white on the valve and let the valve power the boiler and pump up. This way the valve is open so any flow switch would allow boiler to fire up.

 

I do now wonder if the idea is that the bi-pass valve opens and allows water to flow just around the boiler and not around the system, some times the by-pass valve is built in, and some times it's external, if it should be external and it has been missed out, this could be the problem.

I can't find a by-pass valve shown in the boiler, so it would need to be external, it is simply a spring loaded valve so if the motorised valve does not open or all radiator TRV are closed the pump will then lift the valve, instructions for by-pass valve here [/ur] I am an electrician not a plumber, I would guess the valve needs setting? even if fitted if setting too high for pump or it's stuck the it could be why boiler has not fired up.

 

Hi

You have a boiler or Un-cylinder on a balcony? Can you explain please? Are they literally on the balcony?

The frost stat must fire the boiler! These are set to 5'C, if it doesn't fire the boiler it's not wired correctly, don't forget you need a pipe stat connected to the frost stat, it doesn't work on air temp

 

Your the plumber not me, so if the by-pass valve did not work, could it stop boiler firing up, even if wiring is A1?

 

This is my point, if the boiler will only fire up with water flowing then unless a bypass valve opens pump can run, but it is not moving any water, likely damaging the pump. So as far as I can tell remembering I don't know how it is really wired, the problem could well be a plumbing one, with either by-pass valve faulty or missing. So yes it could be there is nothing wrong with wiring.

 

In mothers house it is right next to boiler, and with the boiler she has it was not required as it has one built into the boiler, this is why I am assuming this is the problem, a plumber could think it was built in so it would be easy to miss.

Remember I am an electrical engineer not a plumber, so I was not that involved with domestic central heating, from memory the central heating water pump was magnetic coupled so if it jams it will not stop motor from running but the actual impeller will not turn, and the impeller works on centrifugal force so is limited to pressure it can deliver it is not a positive displacement. So with the valves closed the motor will still be heard to run.

Now if you have pump running and no boiler and you move the bleed lever or leavers on the valve or valves so water can flow and the boiler fires up then you will know that is the problem, no flow, in the past I have seen frost stats which circulated water around the whole house, but because of where yours is, I can see why it only needs to circulate local to boiler, it is possible the plumber also expected the frost stat to heat whole house and never considered it needing a by-pass valve.

I had hoped a plumber would also post, what I don't know is if lifting the by-pass valve on a regular basis is a problem, or if running pump with closed valves is a problem. this U-tube video at around 7 minutes shows the manual leaver.

 

Please say if I have guessed right. I have assumed your plumber and electrician are not fools, so I have looked for a fault which it would be easy to miss. I have just been doing my mothers central heating, and was surprised to find two by-pass valves one external to boiler and one built in. Since your boiler does not seem to have one built in, but I know that some do, it would seem to be an easy mistake for a plumber to make, not fitting one. Also if some one was to look at the system, not having a by-pass valve would not ring alarm bells as often built in.

Any other fault would be easy to find, so simple test is latch the motorised valve to bleed setting, and spray frost stat with freezer fluid and does the boiler start, if so you know what the fault is, so just need a plumber.

 

The way they should work is as follows. Temperature on frost stat drops. Opens motorised valve on heating ,or hot water! Depending if your protecting boiler or pipe work.piepework from boiler warms up, goes round circuit comes back on return which warms up. You have a low set temp pipestat on the return, that will then turn of the boiler again via the closing of the motorised valve.

 

Normally I would agree, however we are looking at a number of things which may have a bearing on that idea.
1) The wiring diagram in the boiler instructions show the frost stat wired across main boiler run terminals, so would not open a motorised valve.
2) Plumber and Electrician had failed to find the fault so not obvious.
3) There is no by-pass valve built into boiler.
4) The boiler is fitted in an area far colder than the house, so frost stat needed more for boiler protection than whole heating protection.
5) The pump runs but boiler does not fire up, yet external circuit would not run pump or boiler independent of each other.
So some thing inside the boiler causes the pump to run without the boiler, this means some safety circuit must have cut in, but that safety circuit does not cut in when normal thermostats call for heat, so something outside the boiler is causing boiler to not fire, and only thing external to boiler I can logically see doing this is the motorised valve not being open.

Now comes the big question should the frost stat be wired to power the motorised valve? This is where it all starts to get a bit of a problem, the boiler may be too cold, but the home may be at temperature required both for room and hot water temperature, so really you don't want the motorised valve opening just to keep boiler warm, also should the valve fail to open there could be frost damage. However if a programmer is stopping the house warming up due to time setting, then you want the house also to be protected from frost.

It would seem likely that two independent frost stats are required, however today not sure if we really want a timer for central heating? Maybe required for hot water, but even with hot water modern storage tanks are so well insulated it could simply be left on 24/7. And using a programmable thermostat instead of timer and thermostat means there is an automatic frost protection in the house.

The first post also says

which is exactly what I am also saying, since you can latch the motorised valve so easy, all one needs to do is latch the valve, if the frost stat then works it is 90% sure a by-pass valve is missing or stuck. Another method could be a towel rail plumbed before the motorised valve, that would allow enough water to flow to allow boiler to fire up, and the towel rail would be warm if either house is cold or domestic water is cold, and it would also put some heat into the house. So there is a 10% chance that the towel rail is the loop and some one has simply turned off the towel rail.

However it does seem this is a plumbing rather than electrical problem, and I am not a plumber, what we need is a plumber to either agree with what I am saying or pull it to bits and present some other reason for the problem. However I am also looking for a reasonable mistake, I am assuming the plumber and electrician know their job, so it needs to be something which could be easy missed, since many boilers today have the by-pass valve built into boiler, not fitting one seems a reasonable mistake to make. One would think the plumber would check things like the valves being closed on a towel rail.