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Post by jubjub on Feb 13, 2020 13:23:39 GMT
Following my recent break in I have now had all the electrics repaired/replaced. The heating system is a Mikuni X40 which the electrian says is great condition so I am keeping it for now.I do want to install a thermostat though as we don't go as often in the colder months. Can anyone recommend a specific make, obviously it would have to be 12v. Thanks
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Post by Telemachus on Feb 13, 2020 13:33:07 GMT
Thermostats are considered a very bad idea for Mikunis. They result in the heater "short cycling", ie turning on for a few minutes or tens of minutes, then off again. That leads to carbon build up and failure within a fairly short time period (maybe a year). It's worse in a boat where, for example, the heater might kick in, then the sun comes out and thus there is a sudden and rapid rise in cabin temperature, so the thermostat clicks off. Then the sun goes in … and repeat!
We do have a programmable thermostat but I set to a very high temperature so it doesn't cut off, and control it by time. In other words, it is more of a timeswitch than a thermostat. I do know of another chap who added a home-made electronic timer so that when the thermostat cut in, the heater would stay on for 1 hour minimum.
If despite all that you still want a thermostat, there is plenty of choice of battery operated models. Ours is battery operated but in 9 years I have only had to replace the battery once, so it is not a significant chore. They typically have just a switch (relay) inside that connects 2 wires together (or not). The technical term is "volt-free contacts" which means the are floating, not tied to any supply voltage.
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Post by jubjub on Feb 13, 2020 13:37:01 GMT
Thanks there is a basic timer switch fitted as all the rads have thermostat valves so maybe best to keep to that?
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Post by Deleted on Feb 13, 2020 13:43:23 GMT
Another option if it is unattended and you are worried about low temperatures would be to fit a GSM gate opener type switch to it so that you can turn it on and off with your phone.
I think there are some which also report the temperature which would be quite handy.
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Post by Telemachus on Feb 13, 2020 13:55:48 GMT
Thanks there is a basic timer switch fitted as all the rads have thermostat valves so maybe best to keep to that? Well once again, as I understand it TRVs are a very bad idea. As the boat heats up the TRVs start to shut down. The heater only has 3 modes, off, maximum or 1/2 power. Once the TRVs shut down to the point where 1/2 power is too much, the heater switches off, then restarts for a short while, after a few minutes cooling it starts up again … and repeat. Every time the heater starts, the glow plug is activated which not only uses about 25A current, but of course shortens its life, and as I mentioned, short cycling leads to rapid carbon build up.
I am saying all this because this is what I have repeatedly heard. Our own Mikuni doesn't have TRVs and I never let it short cycle, so I can't say for sure that it is all correct as opposed to old wives tale!
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Post by jubjub on Feb 13, 2020 13:56:31 GMT
Any idea where I could look at/ buy one?ta
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Post by Deleted on Feb 13, 2020 14:00:13 GMT
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Post by Deleted on Feb 13, 2020 20:25:38 GMT
For the last 18 years on two different boats I have run TRVs with a Mikuni and Eberspacher with no problems of short cycling.
The reason is twofold :
1 both boats have the bathroom radiator that is sans TRV and often one of the others is full up.
2 I rarely run the system for more than three hours at a time, normally switches to low heat at about two hours.
I switch it on about 3 hrs before I get to the boat and all is warm when I arrive.
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Post by Telemachus on Feb 13, 2020 20:31:09 GMT
For the last 18 years on two different boats I have run TRVs with a Mikuni and Eberspacher with no problems of short cycling. The reason is twofold : 1 both boats have the bathroom radiator that is sans TRV and often one of the others is full up. 2 I rarely run the system for more than three hours at a time, normally switches to low heat at about two hours. I switch it on about 3 hrs before I get to the boat and all is warm when I arrive. Obviously if the Mikuni never actually short cycles, it isn’t a problem. But equally, what is the point of you having TRVs? |
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Post by Deleted on Feb 13, 2020 20:40:18 GMT
Because TRV sounds really cool. A bit like TVR. Chimaera and all that lovely V8 noise.
Much better than those Skoda jobbies you (pl) seem to insist on driving.
ETA interestingly my barge was equipped with a large neverspacher no.7 with 3 rads 2 of which had TRVs and a large clorifier. I replaced the neverspacher with a MX40 Mikuni and it did work quite well. The TRVs did seem a bit pointless but quite nice in a way except when they got stuck.
Having a "heat dump" radiator of some sort is worthwhile. Or lots of extra ventilation to keep the rads cool.
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Post by Deleted on Feb 13, 2020 21:28:58 GMT
For the last 18 years on two different boats I have run TRVs with a Mikuni and Eberspacher with no problems of short cycling. The reason is twofold : 1 both boats have the bathroom radiator that is sans TRV and often one of the others is full up. 2 I rarely run the system for more than three hours at a time, normally switches to low heat at about two hours. I switch it on about 3 hrs before I get to the boat and all is warm when I arrive. Obviously if the Mikuni never actually short cycles, it isn’t a problem. But equally, what is the point of you having TRVs? Because it regulates the temperature of the two radiators in the living area otherwise it would get unbearably hot especially when the stove and heating are on, bathroom is better warm, the other rad that is often on is in the corridor just down from the bathroom towards the bedroom, just puts a bit of heat towards the bedroom. Works for me  Oh and at least Skodas are reliable unlike TVR  |
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Post by JohnV on Feb 14, 2020 2:38:14 GMT
Just been reading and not posting on this as don't know owt about Mikuni's (my central heating is a Bubble PJ)
However TRV's as Loddon says prevent certain areas getting too hot. They also give a sensible "spread" of heat through the boat.
I use TRV's with 3 unregulated radiators in areas that require more heating because of heat losses (wheelhouse and corridor to Engine room) or where it's nicer to have more warmth (bathroom) and 5 regulated radiators in the saloon and bedroom areas
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Post by Telemachus on Feb 14, 2020 10:02:47 GMT
Just been reading and not posting on this as don't know owt about Mikuni's (my central heating is a Bubble PJ) However TRV's as Loddon says prevent certain areas getting too hot. They also give a sensible "spread" of heat through the boat. I use TRV's with 3 unregulated radiators in areas that require more heating because of heat losses (wheelhouse and corridor to Engine room) or where it's nicer to have more warmth (bathroom) and 5 regulated radiators in the saloon and bedroom areas Obviously i understand what TRVs are for. But the quandary is that Mikunis don’t like short cycling and Mikunis only operate at full heat, half heat, or off. If the TRVs cause the heater to short cycle, that is bad. If the TRVs don’t cause the heater to short cycle it either means that they are never actually shutting down (so what was the point) or that the heating circuit is vastly over-rated compared to the heater, which means that initially the rads won’t get very hot. I can see the point of perhaps 1 or 2 TRVs in a slightly overrrated circuit, but my point is that in general, having a heating circuit with all or most of the rads with TRVs, is very bad for the heater unless eg the heater is never on for long enough for the TRVs to shut down (in which case what was the point of them). Obviously on a more controllable boiler / one that doesn’t mind cycling, TRVs are great and of course we have them at home on a modulating gas boiler. I am not anti-TRV, I am anti-TRV on a Mikuni heater system. |
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Post by jubjub on Feb 18, 2020 9:39:27 GMT
Thanks to everyone who replied.
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