Advice on oil boiler thermostats

[Steve-T]

I've got a problem with an oil boiler overheating the water, I have a solution and if anybody has any relevant advice, I'd be obliged.

I have a Firebird 90S oil boiler, which was installed about 10yrs ago. It has a Cordice 542788 thermostat fitted, which has a range of 60-90c apparently. The water temperature tops out at 68c when the thermostat is on its lowest setting so either it is not working properly or there is too much leeway in the manufacturers settings.

The problem is that the hot water has damaged the shower pump. The easiest fix being a new thermostat which actually works and a better range.

I have found this on eBay which looks like it might do the job:

Reliance - Dual Combined Control and High Limit Thermostat (30¡C - 70¡C) | eBay

Products will not be covered if misused or not serviced as per maintenance instructions. Useful Link. Ending Soon.

www.ebay.co.uk

I've then had a look at the manufactures and found that the only one that they supply is for a hot water cylinder, although it looks like you can buy copper pockets for it, which I understand to be sensors on wires rather than a ridged spike that goes into the cylinder.

Cylinder Thermostats | Reliance Water Controls

Reliance Water Control's Cylinder Thermostats allow temperature control of central heating systems in domestic & commercial environments.

www.rwc.co.uk

I have contacted Firebird who are of the opinion that the wiring is compatible, I'm just awaiting a reply from the eBay supplier to confirm the length and diameter of the pockets to ensure that they will fit into the boiler.

The industry standard for boilers appears to be 60c< and the for shower pumps its 60c> so there is a very fine line of tolerance. I do understand that stored water should be around 60c to prevent Andy bacteria forming. I'm guessing that Thermostats are juts not very accurate, so having a wider range of operation is surely an advantage to overcome this.

Many thanks in advance,

Steve

 

[SJB060685]

Google imit stat, phials should fit in sleave ok. Can always pack out with thermal paste.

 

[John.g]

I've got a problem with an oil boiler overheating the water, I have a solution and if anybody has any relevant advice, I'd be obliged.

I have a Firebird 90S oil boiler, which was installed about 10yrs ago. It has a Cordice 542788 thermostat fitted, which has a range of 60-90c apparently. The water temperature tops out at 68c when the thermostat is on its lowest setting so either it is not working properly or there is too much leeway in the manufacturers settings.

The problem is that the hot water has damaged the shower pump. The easiest fix being a new thermostat which actually works and a better range.

I have found this on eBay which looks like it might do the job:

Reliance - Dual Combined Control and High Limit Thermostat (30¡C - 70¡C) | eBay

Products will not be covered if misused or not serviced as per maintenance instructions. Useful Link. Ending Soon.

www.ebay.co.uk

I've then had a look at the manufactures and found that the only one that they supply is for a hot water cylinder, although it looks like you can buy copper pockets for it, which I understand to be sensors on wires rather than a ridged spike that goes into the cylinder.

Cylinder Thermostats | Reliance Water Controls

Reliance Water Control's Cylinder Thermostats allow temperature control of central heating systems in domestic & commercial environments.

www.rwc.co.uk

I have contacted Firebird who are of the opinion that the wiring is compatible, I'm just awaiting a reply from the eBay supplier to confirm the length and diameter of the pockets to ensure that they will fit into the boiler.

The industry standard for boilers appears to be 60c< and the for shower pumps its 60c> so there is a very fine line of tolerance. I do understand that stored water should be around 60c to prevent Andy bacteria forming. I'm guessing that Thermostats are juts not very accurate, so having a wider range of operation is surely an advantage to overcome this.

Many thanks in advance,

Steve

I have one of those boilers (15 years) as well with a Imit boiler stat, its range is 65C/85C and is very accurate, I generally run my boiler at 70C but I have a motorized valve/cylinder stat on the HW cylinder set to 60C, you seem to be running your cylinder uncontrolled so this is why you have to control its temp with the boiler stat?, it's still a bit surprising though that the pump is damaged by 65/68C hot water temperatures as the manufacturers are well aware that the temperature must be > 60C for legionella protection.

 

[SimonG]

I have one of those boilers (15 years) as well with a Imit boiler stat, its range is 65C/85C and is very accurate, I generally run my boiler at 70C but I have a motorized valve/cylinder stat on the HW cylinder set to 60C, you seem to be running your cylinder uncontrolled so this is why you have to control its temp with the boiler stat?, it's still a bit surprising though that the pump is damaged by 65/68C hot water temperatures as the manufacturers are well aware that the temperature must be > 60C for legionella protection.

Pump manufacturers specify water must be below 65C. Anything above that distorts the impellors. Seen it a few times.

Cant see why pump manufacturers cant design for hotter temps.

 

[Steve-T]

I have one of those boilers (15 years) as well with a Imit boiler stat, its range is 65C/85C and is very accurate, I generally run my boiler at 70C but I have a motorized valve/cylinder stat on the HW cylinder set to 60C, you seem to be running your cylinder uncontrolled so this is why you have to control its temp with the boiler stat?, it's still a bit surprising though that the pump is damaged by 65/68C hot water temperatures as the manufacturers are well aware that the temperature must be > 60C for legionella protection.

The cylinder is quite old with no separate thermostat for boiler heated water sadly.

I take your point about the shower pumps failing with such a small margin, very frustrating!!

It may be that my stat is working within the parameters that it should e.g. +/- 10%, however the shower pumps appear to have much finer tolerances. To that end, my thinking is get a stat that has a far greater range above and below 60c then I should stand a better chance of actually achieving the correct temperature.
[automerge]1586868532[/automerge]

Pump manufacturers specify water must be below 65C. Anything above that distorts the impellors. Seen it a few times.

Cant see why pump manufacturers cant design for hotter temps.

I can see a market for boiler manufacturers to make shower pumps that work with their kit!!!!
[automerge]1586868704[/automerge]

Google imit stat, phials should fit in sleave ok. Can always pack out with thermal paste.

The Imit Stat is pretty much ident with what I've got. If the lowest setting is 60c and there is some leeway in the setting, then the water could got higher and I would be in the same position. If I get the Reliance unit, it affords more temperature control unto and around 60c.

 

[SimonG]

Convert cylinder to fully pumped. 2 port valves, cylinder stat and room stat. S plan.

 

[SJB060685]

You need independent thermostatic control of heating and hot water. As above before looking to replace the dual stats at the boiler look into a fully pumped system, or at least a c plan

 

[Ric2013]

I think you're going to be disappointed with that high limit stat clipped to the boiler flow. Depends how quick it is to react. May be okay if if has a mercury phial.

I once tried to govern a boiler, that had a very high hysterisis internal thermostat, using the Honeywell pipe stat (which was a basic bimetallic cylinder stat which clips to a pipe). The problem was that the boiler raised the water temperature faster than the Honeywell stat could react. So the boiler would overshoot before the stat became aware of it. If it set the Honeywell stat lower, it would prevent overheating, but then the boiler had to run almost stone cold before the stat would allow it to refire. Eventually it turned out that the boiler internal thermostat, thought to be obsolete, was available, and replacement solved the problem.

I would agree with others that the solution would be to fit a thermostat to your water cylinder and convert to fully-pumped. It'll be of the cheap and nasty bimetallic strip design, no doubt, but the quantity of water involved means that the stat will have time to gauge the temperature. You'll find a cylinder stat may not be especially accurate to the marked settings, but once you have got the setting where you want it to be, it should be surprisingly consistent.

 

[John.g]

Would one of these TapStats (I think they are called) be a cheap(er) option if the HW temperature is the only concern, these connect directly via the strapped on cylinder stat to a valve fitted in the cylinder coil and have no other (electrical or otherwise) requirements. Drayton controls make them.

 

[SJB060685]

Would one of these TapStats (I think they are called) be a cheap(er) option if the HW temperature is the only concern, these connect directly via the strapped on cylinder stat to a valve fitted in the cylinder coil and have no other (electrical or otherwise) requirements. Drayton controls make them.

Looking at the specs John i can't see how this cuts power to burner? Although this will govern the HW temperature if its not cutting power to burner then you will still get cycling with nowhere for the heat to go, unless the 3 way also acts as a bypass?

 

[John.g]

No, it won't cut power to the burner but I was under the impression that there are no controls on the boiler apart from a on/off switch and maybe a timed on/off so the whole system, CH+HW), runs as one?.

 

[SJB060685]

His current setup is gravity HW and pumped CH. At present when the programmer comes on for HW that's a direct live to burner and no temperature control other than boiler stat governing HW temperature. When the programmer comes on for CH it brings on HW as well for live to burner and the roomstat just controls the pump, a very primitive and dated way of doing this. In the back of the programmer there will be a plug for fully pumped or gravity.
He needs to consider updating to fully pumped with independent control or at least a C plan as I mentioned above, both get rid of the short cycling

 

[Steve-T]

I think you're going to be disappointed with that high limit stat clipped to the boiler flow. Depends how quick it is to react. May be okay if if has a mercury phial.

I once tried to govern a boiler, that had a very high hysterisis internal thermostat, using the Honeywell pipe stat (which was a basic bimetallic cylinder stat which clips to a pipe). The problem was that the boiler raised the water temperature faster than the Honeywell stat could react. So the boiler would overshoot before the stat became aware of it. If it set the Honeywell stat lower, it would prevent overheating, but then the boiler had to run almost stone cold before the stat would allow it to refire. Eventually it turned out that the boiler internal thermostat, thought to be obsolete, was available, and replacement solved the problem.

I would agree with others that the solution would be to fit a thermostat to your water cylinder and convert to fully-pumped. It'll be of the cheap and nasty bimetallic strip design, no doubt, but the quantity of water involved means that the stat will have time to gauge the temperature. You'll find a cylinder stat may not be especially accurate to the marked settings, but once you have got the setting where you want it to be, it should be surprisingly consistent.

Thanks for all the replies thus far.

It appears the only replacement thermostat is another firebird unit because of the length of wires to the probes:

My understanding is that most of these dual thermostat units have a leeway of +/- 0.5c so I would imagine fitting a new unit would solve the problem.......alas you have had experience of the boiler heating up the water faster than the thermostat can react to, so this fix might not work.

A understand that the system is old in design so a new cylinder with separate thermostat valves for the hot water would be the answer, but the is not an easy fix during Covid-19 and I'd imagine I'd be throwing £1000 at the problem too.