webasto help please

[Soupdragon]

I have a webasto thermo top c and it has been working fine until I removed a radiator from the system. The heater has been very temperamental since, the worst fault is that it will only run for an hour at a time it will work if I switch it on after it switches off. I have asked an engineer and his advice was bleed the system which I have done several times but the problem still remains. Any help with this would be good thanks.

[NMEA]

Sounds like it was marginally loaded with the radiators you had and removing one has "broken the camel's back". the things must be well loaded otherwise will heat the coolant to a temperature where the heater shuts off as the rads can not get rid of the heat fast enough. What is the size and type of radiators: it 1) served 2) now serves.

[Soupdragon]

I removed an unregulated rad from the bedroom but the system has 4 rads that are thermostat regulated a d 2 unregulated still in operation, the 2 unregulated rads are either side of the stern door it is also connected to our immersion tank which is quite a size 120 litres. The sizes of the rads are 2X 3ft x 11 inches 1x 4ft x 2ft and 1x 2.6ft x 11inches. The 2 unregulated are18 inch square. Researching the boat has told me that the fit out was bespoke with a lot of things being made to measure and it had a alde heater which has been removed according to the bsc paperwork that came with the boat when I bought it.

[NMEA]

Right, first thing's first, under no circumstances should thermostatic valves be used with an evaporator heater, they cause cycling, unwanted shut downs and premature coking, remove and replace with standard valves or at the very least open them to maximum temperature and leave them there. It sounds like you have may have enough load but check the sizes you have against similar radiators advertised output, (Screwfix catalogue is as good a source as any) make sure you are checking like for like, i.e. single panel, double panel, single fin , double fin etc. and be sure they come to at least 6kw, you can ignore the calorifier regardless of capacity. Perhaps a little more info on the system, is it pressurised or hopper, if hopper is it a feed and return type or a simple single pipe bleed from the feed or return.

[Soupdragon]

System is not pressurised it has a header tank fitted above cylinder the bleed valve is fitted to the flow from the heater and there is a valve on the pipe in the bathroom wich seems to bleed this part automatically as it works on filling and occasionally when the system is working as I only bought the boat 2 years ago and am slowly coming to understand the workings.

[smileypete]

Since the low output of the Thermo Top C is 2.5KW, I'd make sure that at least 3kW of rads are running unregulated.

 

To give some idea that's equivalent of nearly four 2'x2' double rads (Type 21) which is a fair amount, all the rads will still need balancing (google 'radiator balancing') using the lockshield valves.

 

Might be some clevuh way of using a buffer tank or even calorifier to reduce cycling, but probably best to 'keep it simple'...

 

cheers, Pete.

~smpt~

Edited September 22, 2014 by smileypete

[Soupdragon]

Thanks everyone I have taken the advice and have ordered new rads.

[NMEA]

What type, 21 or 22, the 22s will shift a bit more heat from the system size for size, also another thought occurred to me and it was remis of me not to ask at the outset, what strength of anti freeze are you using, if any, it may sound an odd question given the OP but humor me.

[Soupdragon]

Sorry been working nights but the rads all 5 of them have arrived and they come from the screwfix catalogue and are barlow round tops allegedly of type 22 whatever this is. In humouring you, you might get annoyed when I say when I took out the other rad I never put any inhibitor in the system but I have bought a litre to put in for the new rads.

[NMEA]

The reason I asked about the antifreeze is that if you had increased the concentration it may have caused the heater to cycle (switch off) more often as it is not very efficient in removing heat from the exchanger at high concentrations. If you are using water and inhibitor then frost protection apart it will be more efficient.