Advanced search

Boiler - plumber says wired incorrectly and no thermostat on hot water cylinder

(9 Posts)
LittleBlueShoes Wed 20-Jan-16 10:00:44

I am hoping PigletJohn or other knowledgeable about boilers people are about and can help me. Sorry if this is longwinded.

We moved into this house October 2014, boiler is a Vaillant EcoMax Pro open vented system, fitted in 2006. In the summer we were just about to organise its first service (it had been serviced in May 2014 by previous owner. Boiler had been performing fine but had begun to sound a bit rattly on starting up and was becoming a bit noisier) when we had to have our electricity meter replaced. So I turned boiler off and turned off the wall switch which had been pretty much continuously on while that was taking place but and when I turned it back on the boiler wouldn't restart/no sign of life on the control panel.

I called out a plumber I had used before (gas safe etc, lots of people locally use, I had used him for services on Worcester-Bosch combi boiler in our old flat but he had plenty of experience with Vaillant) and he thought it was perhaps the actual electrical switch as I had noticed it had been a bit temperamental in the past (once I had turned off boiler and switch needed flicked a couple of times before boiler came back on). So he replaced that, boiler still dead. So he thought it must be the PCB. He called Vaillant, said they thought the same. Replaced both PCBs (he said it would be difficult to know which one was faulty so better to replace both) and boiler worked again but sounded even noisier than before. He thought it was the fan and that had perhaps triggered the other problems. Replaced fan. It sounded much better though not as great as our old boiler. I thought perhaps that was normal with a conventional, older boiler as we had had a fairly new combi before.

With all the fuss I couldn't face getting him back to service it and thought it would wait. Boiler started sounding really noisy again in December and worse during recent cold spell (we are in Scotland) so yesterday got a new plumber out who is Vaillant accredited. He immediately said that the boiler has been incorrectly wired. The pump is not wired directly into the boiler (only one cable going in underneath. He also noted that the hot water cylinder has no thermostat. He said this will be resulting in the pump not being able to cool down properly. Another problem I had noticed is that the cold water tank in the loft seemed to be refilling a lot. He said that it is probably because of this wiring problem with the pump and that if I put my hand in the water up there it would probably be warm (I am a wuss so haven't done this). He said that probably when boiler was installed the fitter did not put in new wiring and just kept the old wiring. He said it would need a full rewire, about a days work, lifting some floorboard etc. He's going to get back to me with a quote. I seemed to know what he was talking about but I feel really insecure that previous plumber didn't spot this. Does it all sound likely??? Thanks so much for your help. Wasn't sure whether to get another plumber in as don't want to waste plumbers time when I will probably get the work done by this guy if it is what is needed. Also, would it be better to just upgrade the whole system or is this work worth doing? Boiler is now 10 years old and we spent £650 on it last year with the PCBs and fan etc. We had been thinking of eventually replacing it with a closed-vented system so we could get rid of the cold water tanks in the loft.

LittleBlueShoes Wed 20-Jan-16 11:06:10

Just to add, we have always had scalding hot water and couldn't work out how to lower the temp independently of the heating. Plumber says that the rewire will enable him to sort this out. He also suggested replacing the pipe coming out of the bottom of the hot water cylinder as it is too narrow and said that some of the noise might be from kettling/debris in system so he is also going to quote for fitting a filter. I don't know if these will be useful but I am including pics of the hot water cylinder and the wiring under the boiler.

PigletJohn Wed 20-Jan-16 12:36:12

yes, there should be a thermostat on the cylinder, to direct heat for the HW when it is required (and not when it is not).

It should be wired so that it operates a motorised valve. The room thermostat should also operate this valve, and the valve should turn on the pump when either radiators or cylinder need heating.

There appears to be a motorised valve in your picture, it looks as if it turns the radiator circuit on and off. You will need either a different, or an additional, valve to control the cylinder.

This will prevent your hot water getting scaldingly hot, and will reduce gas usage, especially in summer.

I agree that fitting a filter is a good move, as yours is an older open-vented system. Make sure he shows you how to empty the dirt out of it, and that you practice before he leaves. It is no harder than emptying a hoover bag or a dishwasher filter. I recommend that you also give it a chemical clean, you can do that after the filter is fitted and it will probably dislodge a lot of dirt and sediment. It is very satisfying to clean this out of the filter, almost as good as picking wax out of your ears. If you still have a bad problem afterwards you may need a professional clean ££££.

You will need to go into the loft and find the feed and expansion tank. It will probably be black plastic, about 18"x12"x12" and have a ballcock in it like an old WC cistern. There will be mud in the bottom which you are going to bale out into a bucket, you will then sponge out the tank and wipe it round with bleach. Come back later when you have mentally prepared yourself.

You should also fit some pipe lagging on those exposed pipes. I expect they are mostly 22mm o.d. and a few 15mm. Measure a couple and you will recognise by eye. If you have a very old system you may have some 28mm which is hard to find. It is a very easy DIY job, you cut it to size with a breadknife. Do it after the alterations have been done. Your cylinder is about 25 years old and coated with yellow foam which is not up to modern standards, get a red cylinder jacket as well (leave the immersion cap uncovered) and save more money.

These DIY jobs are easy but take time, so will cost if you have to pay someone. They need no particular skill.

PigletJohn Wed 20-Jan-16 12:56:17

jacket cheaper here and available for collection or delivery

LittleBlueShoes Wed 20-Jan-16 13:13:57

Thank you so much PigletJohn for your reply.

The gas engineer who came yesterday plans to rewire the HW tank directly into the boiler. He says this is necessary for a Vaillant and that he thinks when the new boiler was installed the wiring was not upgraded correctly at the time. He noticed this immediately as there is only one cable going into the bottom of the boiler. Does that sound right? I think he might have also referred to replacing the valve on the HW tank but I am not very sure so I will check that with him. He recommended upgrading the piping coming out of the bottom of it too (he said it was too narrow) - do you think that is worth doing? Also fitting a thermostat to the tank, he said as you have that this would sort the problem of the hot water. Our room thermostat appears to work (ie when I turn it down the boiler seems to turn off etc) but he didn't check it (although he did ask did we have one and looked relieved that we did!). Yes, our tank is probably about 28 years old as that is when the house was built. I will order the jacket and lagging. Is the immersion cap the round red thing at the top? I will have to work myself up to the expansion tank job. Should I do that before the work is done? Should I turn off the system completely to do it (heating it currently off on the timer but do I need to turn the electrical switch off too)? How much roughly should I expect the filter to cost (ie is it lots of money)? Do you think that the system is worth the work ie do you think it is a decent system for a small three bed one bath house and will last a few more years??

LittleBlueShoes Wed 20-Jan-16 13:18:55

I have been up the loft and found the expansion tank. It has a ball cock as you described and is about half full. Water looks greyish and sludgey. Will have to work myself up to it. Thank you for all your advice.

PigletJohn Wed 20-Jan-16 13:57:37

the filter is certainly worth having. It will cost about £100 plus fitting. If he is going to fit a new valve, as I expect, then it would be the best time to upgrade the small pipes to larger, although I would also suggest fitting a gate valve so the cylinder can be balanced against the radiator load. It will cost little extra, done at the same time.

You can clean out the f&e before or after the work. Before would be better. You tie the float up so it does not refill with cold water while you are working. You may find a nail in the roof timbers above where a piece of string was tied last time. There should be a plastic lid on the tank to keep dirt and wildlife out. If the water is warm that is a bad sign, but your chemical clean may improve it if it is caused by soft sludge in the pipes.

I think perhaps you new heating engineer is better than your old one, as he spotted the problem and diagnosed the cause. People who change parts without knowing where the fault is sometimes cost more in repeat calls. Tell him you are thinking of doing a chemical clean after the filter is on. Say you hear X400 is suitable for DIY and ask him to show you the drain cock.

PigletJohn Wed 20-Jan-16 14:09:40


Cleaning out the expansion tank, I suppose you ought to turn the boiler off, or it might gurgle a bit, but no need to do more. It will not do any harm either way, as long as you untie the float when you have finished.

The reason for cleaning it out is so that the sludge does not flow down the pipes and make the system dirtier than it already is. There may also be bacteria or fungus in it, and wiping round with bleach and fitting a lid will help. A plastic mug and a big sponge are good for baling it out.

There should also be a lid on your big tank, this is even more important as you brush your teeth in it. If not measure it and ring round local plumbers merchants.

Unless your engineer disagrees, you will need a litre of X400, and of X100, and, if you are in a hard-water area, of X200. They are mild chemicals and suitable for DIY work.

LittleBlueShoes Wed 20-Jan-16 14:23:58

Thank you again. Both tanks have lids (also both have padded insulation all the way round them). All the pipes in the loft appear to be lagged too. The big cold water tank seems huge, even possibly two tanks if that is possible? - not floored in that part of the loft but seems to go back a long way, but I suppose that is normal? The main thing is that you agree with the second heating engineer so I feel confident to get on with getting the work done and I will ask him to check over the entire system and make sure it is all up to scratch. Thanks very much for the tips on cleaning the tank and adding the jacket and cladding. I had noticed that the HW tank seemed to give off huge amounts of heat and that didn't seem right. I can see why now. Hopefully at least the gas bill will go down a bit!

Join the discussion

Registering is free, easy, and means you can join in the discussion, watch threads, get discounts, win prizes and lots more.

Register now »

Already registered? Log in with: