Room thermostat replacement

fat-tony

I have a conventional oil-fired central heating system (house is 30 years old). The burner was replaced about 6-7 years ago with a Bentone B10 model. The time-switch is mechanical and ready for the scrapheap.
I am going to replace the timeswitch and room thermostat with a new programmable thermostat.
The issue I'm facing is that the existing Satchwell room thermostat is rated at 16 amps. It switches the live feed from the time-switch to the burner and water pump. Most of the LCD programmable thermostats I've researched seem to be rated at 3 amps or maybe 5 amps. From what I can see in the user manual for the Bentone burner it specifies a maximum fuse rating of 10 amps for the supply, but it does not give me any details of the starting current or running current.
I'm concerned that the current draw for the burner and pump may be too high for most of the programmable 'stats available, given that the existing thermostat is rated at 16 amps.
Does anyone have practical experience of using one of these new battery powered thermostats with a conventional oil burner and can ease my concerns?

ntpm

fat-tony wrote: »

I have a conventional oil-fired central heating system (house is 30 years old). The burner was replaced about 6-7 years ago with a Bentone B10 model. The time-switch is mechanical and ready for the scrapheap.
I am going to replace the timeswitch and room thermostat with a new programmable thermostat.
The issue I'm facing is that the existing Satchwell room thermostat is rated at 16 amps. It switches the live feed from the time-switch to the burner and water pump. Most of the LCD programmable thermostats I've researched seem to be rated at 3 amps or maybe 5 amps. From what I can see in the user manual for the Bentone burner it specifies a maximum fuse rating of 10 amps for the supply, but it does not give me any details of the starting current or running current.
I'm concerned that the current draw for the burner and pump may be too high for most of the programmable 'stats available, given that the existing thermostat is rated at 16 amps.
Does anyone have practical experience of using one of these new battery powered thermostats with a conventional oil burner and can ease my concerns?

If you have separate zone control/ if pipework is zoned.
Usually the set up is to use the motorized valves auxillary switch (heating and hot water circuits) to switch over a perminent live on to the burner/pump.

For you info: Pump and burner only usually draws 2-3 Amp max that is why most manufactures insist on Fused spur double pole isolation) fuse rated at 3 or 5amp.
Therfore the programmable thermostat can be used but it is not ideal.

fat-tony

No zones, no motorised valves - just a gasoil burner and a circulating pump:)

I'm not sure how to interpret your second paragraph:

"For you info: Pump and burner only usually draws 2-3 Amp max that is why most manufactures insist on Fused spur double pole isolation) fuse rated at 3 or 5amp.
Therfore the programmable thermostat can be used but it is not ideal. "

The pump and burner are on a separate fused spur all right. If the pump and burner only draw 2-3 amps (thanks for that info - it confirms my initial research), then why is the programmable thermostat "not ideal"?

ntpm

fat-tony wrote: »

No zones, no motorised valves - just a gasoil burner and a circulating pump:)

I'm not sure how to interpret your second paragraph:

"For you info: Pump and burner only usually draws 2-3 Amp max that is why most manufactures insist on Fused spur double pole isolation) fuse rated at 3 or 5amp.
Therfore the programmable thermostat can be used but it is not ideal. "

The pump and burner are on a separate fused spur all right. If the pump and burner only draw 2-3 amps (thanks for that info - it confirms my initial research), then why is the programmable thermostat "not ideal"?

Sorry for confusion:
Ideal situation is for Energy Efficient Controls.
Separate time and temperature control for Hot water and Heating Zones with "Boiler interlock". ie. the boiler only runs if the thermostat(s) request heat.
You current set up means you do not have temperature control on hotwater/ cylinder. This means hotwater is probably getting too hot and utilising heat/ oil that may be making your system less efficient.

Check the Boiler/ pump fused spur has a 3Amp fuse in it. Electricians normally leave 13Amp in it.

fat-tony

Ok thanks - that's clearer. The circuit to the boiler is actually on a 20A cartridge fuse (remember, this was done when the house was built in the '70s;)).
I agree that the hot water in the cylinder is probably wasted, but I have the flow to the coil restricted so that most of the heat goes to the rads.

The main thing, from what you say, is that the burner is not consuming a lot of electricity, so I can purchase a thermostat with a 3A or 5A relay, then? I was concerned that the inductive load generated by the burner motor/fan on startup would be too much for the new 'stat. The old 'stat, with its 16A capacity is overkill, perhaps?

ntpm

fat-tony wrote: »

Ok thanks - that's clearer. The circuit to the boiler is actually on a 20A cartridge fuse (remember, this was done when the house was built in the '70s;)).
I agree that the hot water in the cylinder is probably wasted, but I have the flow to the coil restricted so that most of the heat goes to the rads.

The main thing, from what you say, is that the burner is not consuming a lot of electricity, so I can purchase a thermostat with a 3A or 5A relay, then? I was concerned that the inductive load generated by the burner motor/fan on startup would be too much for the new 'stat. The old 'stat, with its 16A capacity is overkill, perhaps?

Most stats will be ok. Inductive load of fan motor and circulating pump not an issue.
Older stats and timers were a lot more robust in design and were used to switch power for larger components in commercial situations.

Electrical safety:
As your heating is supplied by a 20Amp you should also have a fused spur on the supply cable before the timeclock and stat and heating wiring as the components and cabling is not protected.
Normally a straight forward job.

fat-tony

Top man ntpm! I had come to the conclusion myself that the original 'stat was somewhat over-engineered, but there was still a nagging doubt that it was capable of 16A switching for a reason.

My plan is to take out the existing time-switch (and on/off light switch which isolates the burner), which is mounted on a timber frame standoff in the boiler house, with an appropriately fused spur with a switch. The live loop to the new programmable thermostat will be linked to the burner and the pump.

M cebee

as ntpm said the 'digital' stuff will be capable of switching a burner/pump direct usually

but they're better to form part of a control cct if possible-and have the mv's or a relay switching pump/burner

just make sure you isolate 'all lives' with an isolating switch beside boiler

mazthespark

if your worried about the load that the thermostat will be switching you could use the thermostat to switch a relay which in turn switches on the boiler and pump

fat-tony

Thanks for the suggestion but I wanted to keep the complexity to a minimum. In the end I bought a Salus RT500 and it is working perfectly with my set up:)