Truma UltraHeat

This may been covered earlier but I will ask anyway.
Last night whilst we staying at a Britstops Pub it got a bit chilly so we put the heater on gas. Lit first time and was working ok until we went to bed.
This morning the bathroom felt a bit chilly so I thought I would put the heating back on for managements shower and air the towels.
Tried lighting the heater but it wouldn’t light. There was no sound from the igniter but the fan was running. I knew the gas was ok because the water heater was on and I had made a brew.
Stopped for lunch between stopovers and tried the heater. It now lights every time.   This must prove the igniter battery is ok. 
The leisure batteries are on the to change list but before  I dash out and buy batteries or an igniter control box at silly money prices any thoughts would be appreciated.

Our heater is tempremental too.  I'm not sure whether the ignitor is powered by the leisure battery, or by a separate replaceable battery.  "The book" explains how to replace the ignitor battery, but I have had the front off the heater and can't see one to replace.  For me, if it's "ticking", it's working.

I think the fault with ours might be an innefficiency in the flue.  Ironically, it doesn't like starting up in cold and windy weather.  I think you might be able to get flue extensions.  Our flue has a ninety degree bend near the top (which would be very much frowned upon in domestic natural (not fan-assisted) flues).

What happens with ours is that the pilot lights OK, and then the main burners, but after a short time it all gets too much and the flames fade.  It seems to me like a lack of fresh air, and it runs out of that nice oxygen stuff.  I'm not sure whether the fresh air is taken from the habitation space, or from a hole in the floor under the heater (or both!).  You could do worse than taking the front off and giving it all a gentle hoiver to get rid of the cobwebs.  If it is anything like lighting open fires (at which I am hopeless!) it might help to open the hab door until it gets going.

We took ours to a dealer to look at, but it started OK on that day.  They left it running for a while, using lots of our gas, told us it was OK, and gave us a bill.

Nick

It appears heaters in motorhomes can be fickle at times. Ours is working as it should be now. Because it’s lighting every time now I think that rules out the battery in the igniter.
The only difference yesterday it was overcast at breakfast time but by lunch time was we had driven for a while and we had full sun on the solar panels meaning the leisure batteries were fully charged.
Last night whilst on hook up it worked  as it should do. Of coarse we don’t need it on hook up having the electric heating but sometimes we boost the heating with gas.
I think I may have answered my own question but it was worth seeing iff anyone had any other theories. This year end might be a time to spend money on the old girl. Next week I am going to get a quote for repairing the o/s wheel arch. It  looked badly bodged before we bought the motorhome but now it’s looking really tatty, lowering the appearance some what.

The combustion chamber is under the floor as can be seen in the photo. A lead goes from the ignition box that includes a battery through the metal floor plate to the ignition electrode in the burner. Over time the insulation of that lead deteriorates and can intermittently short out the spark voltage.

Not relevant in this case but driving on excessively wet roads can get water into the combustion chamber and prevent sparking.

A follow up regarding the heater in our Rienza. Annoyingly it has working fine since I asked the question. The last night we were away we were off grid and the leisure battery was quite low according to the reading on the control panel in the morning but the heater lit straight away . 
Thanks for the response folks. I have just got the quote for repairs to the front wheel arch repair, £700, so the heater had best behave it’s self until I have recovered from that.