Advice on oil boiler thermostats

[Steve-T]

Gents, thanks for all your advice, I've gone for a TMV as the solution rather than mess around with the boiler thermostat.

Having spoken to the Firebird, they declared that their thermostat (60-90c) usually worked at 65-78c with a +/- 3c tolerance. It's a bit like using pig iron on a job that requires titanium to that end, my thermostat might have been working 'correctly'.

The TMV is currently pushing out 41c water through the shower via gravity. This might change once the Stuart Turner 3.0 bar pump is installed upon its arrival.

 

[John.g]

The problem I've seen with gravity fed TMV's is that they restrict the flow rate, I assume that you are installing a double ended shower pump and that you are increasing the hot end temperature from 41C to ~ 50/55C to mix with the cold water in the shower mixer or are you just installing a single ended pump to just pump the 41C water through the shower?. Whichever, I would suggest ensuring that the flow rate from the TMV is adequate for your requirements as a 3 bar pump will give/require a very high flow rate.

 

[Steve-T]

The problem I've seen with gravity fed TMV's is that they restrict the flow rate, I assume that you are installing a double ended shower pump and that you are increasing the hot end temperature from 41C to ~ 50/55C to mix with the cold water in the shower mixer or are you just installing a single ended pump to just pump the 41C water through the shower?. Whichever, I would suggest ensuring that the flow rate from the TMV is adequate for your requirements as a 3 bar pump will give/require a very high flow rate.

I have been in dialogue with Stuart Turner, who have recommended the 3.0 bar pump based on the system/pipework that we have..::

Sadly - This forum won't allow me to upload a diagram of what was sent to them

​

Hot Water Cylinder ========= 3m (22mm)========== PUMP ======== 2m (15mm)
||
||
||
||
2m (15mm)
||
||
||
||
SHOWER​

Hopefully this will format, basically the hot water cylinder is 3m from the existing pump site, with 22mm pipe. The pipe reduces to 15mm just before the pump and continues a further 2m and then turns right (90 degrees) and continues another 15mm to the 20x20cm shower head.

They recommend that the pump is located as close to the hot water cylinder as possible, which is where it now is. The old pump was there prior to this new bathroom. The reason for relocating into the bathroom was because the airing cupboard/hot water cylinder is located in my daughter's bedroom and way back when I was getting up at 4.30am...not that she complained about the pump noise!!! The airing cupboard also negates issues with boxing the pump in and air flow.

The old pump was gravity fed by 22mm hot and cold from the airing cupboard to shower mixer (virtually same location) mixed and then sucked back by the pump along another 22mm pipe to the pipe and then pumped back to the shower head under pressure along a further 22mm pipe. Apparently new shower mixer units of this design are hard to find, hence the change. Yup.....hindsight would advice to use two of the 4 existing 22mm pipes for a new pump at one end and new shower mixer at the other

The new pump is a Stuart Turner (ST) Monsoon 3.0bar Twin Universal, as we need a negative head pump. They recommend 3.0 bar because of the distance, reduction from 22>15mm halfway along the length and also a few twists and turns where the old pump was removed the 15mm pipework rejoined.

The gravity flow was deemed to be sufficient by ST, with discussions about pumps pushing water not pulling it, hence the pumps is better off being at one end of 6m rather than in in the middle. Concerns were raised about the the extra pressure at 3.0bar draining the tank, however they explained flow v pressure, stating the pressure increases not the flow, so it should be fine. They were aware of the TMV too and the restriction from 22 to roughly 15 through the valve, by nature of its design.

Anyway, the long and the short of it all is that the system works fine!!

The max water temperature is 44.5c at the shower head. The 38c safety limit is at 38.6c so no drop in water temperature from the TMV. The pressure is efficient and not excessive. the noise is around 62dB compared to the Salamander CT60BU pump at nearly 80dB........the difference between somebody talking to you or shouting at you.

Three showers were had concurrently this morning, two were female with hair washes and at the risk of balancing the sexism, mine was with that just for men hair dye shampoo stuff that you either know about or will do someday (leave in for a minute before rinsing) All showers were run on the 38c setting without need to increase the temperature due to hot water usage.

Changing the boiler thermostat was not the correct way to go. Oil boilers just aren't made to be that accurate, hence you need some better kit like a TMV.

​

 

[SJB060685]

So you've installed a temperature mixing valve to solve your problem? The problem with any thermostat is the hysteresis, hence the +/- factor. Unfortunately a lot of these stats use gas or liquid which expand a certain amount at set temperatures to cut it in and out, there will always be a degree of lag

 

[John.g]

I have been in dialogue with Stuart Turner, who have recommended the 3.0 bar pump based on the system/pipework that we have..::

Sadly - This forum won't allow me to upload a diagram of what was sent to them

​

Hot Water Cylinder ========= 3m (22mm)========== PUMP ======== 2m (15mm)
||
||
||
||
2m (15mm)
||
||
||
||
SHOWER​

Hopefully this will format, basically the hot water cylinder is 3m from the existing pump site, with 22mm pipe. The pipe reduces to 15mm just before the pump and continues a further 2m and then turns right (90 degrees) and continues another 15mm to the 20x20cm shower head.

They recommend that the pump is located as close to the hot water cylinder as possible, which is where it now is. The old pump was there prior to this new bathroom. The reason for relocating into the bathroom was because the airing cupboard/hot water cylinder is located in my daughter's bedroom and way back when I was getting up at 4.30am...not that she complained about the pump noise!!! The airing cupboard also negates issues with boxing the pump in and air flow.

The old pump was gravity fed by 22mm hot and cold from the airing cupboard to shower mixer (virtually same location) mixed and then sucked back by the pump along another 22mm pipe to the pipe and then pumped back to the shower head under pressure along a further 22mm pipe. Apparently new shower mixer units of this design are hard to find, hence the change. Yup...hindsight would advice to use two of the 4 existing 22mm pipes for a new pump at one end and new shower mixer at the other

The new pump is a Stuart Turner (ST) Monsoon 3.0bar Twin Universal, as we need a negative head pump. They recommend 3.0 bar because of the distance, reduction from 22>15mm halfway along the length and also a few twists and turns where the old pump was removed the 15mm pipework rejoined.

The gravity flow was deemed to be sufficient by ST, with discussions about pumps pushing water not pulling it, hence the pumps is better off being at one end of 6m rather than in in the middle. Concerns were raised about the the extra pressure at 3.0bar draining the tank, however they explained flow v pressure, stating the pressure increases not the flow, so it should be fine. They were aware of the TMV too and the restriction from 22 to roughly 15 through the valve, by nature of its design.

Anyway, the long and the short of it all is that the system works fine!!

The max water temperature is 44.5c at the shower head. The 38c safety limit is at 38.6c so no drop in water temperature from the TMV. The pressure is efficient and not excessive. the noise is around 62dB compared to the Salamander CT60BU pump at nearly 80dB....the difference between somebody talking to you or shouting at you.

Three showers were had concurrently this morning, two were female with hair washes and at the risk of balancing the sexism, mine was with that just for men hair dye shampoo stuff that you either know about or will do someday (leave in for a minute before rinsing) All showers were run on the 38c setting without need to increase the temperature due to hot water usage.

Changing the boiler thermostat was not the correct way to go. Oil boilers just aren't made to be that accurate, hence you need some better kit like a TMV.

​

Good to know that the TMV is supplying sufficient flow for your needs, would you mind posting a link to it please.
You might also indicate its location relative to the cylinder/pump.