GLOWWORM COMBI 100E - FLUCTUATING WATER TEMPERATURE

[kilrail]

I wonder if anyone has any idea what my problem might be. I had my boiler serviced in July and it seems like it has not been quite right since. Cold radiators (at the bottom) on previously perfectly balanced system was the first noticeable symptom. Then our shower (a Mira Excel) which used to deliver hot water (strangely without moving out of the blue but that is a different issue), started to fluctuate between lukewarm and cold - no hot even if I moved the dial to red and bypassed the safety.
Stupidly, I assumed at this point that there was a shower problem (I put the rads down to getting out of balance somehow) so I purchased a cartridge £100 for the shower and fitted it and guess what - no change.
This was when I did what I should have done in the first instance and carried out more investigation.
I noticed that when I turn on the hot water tap on a medium flow the water temperature fluctuates between hot and lukewarm. This is the part I'm not sure about, should the gas burners stay burning when the hot water is running or is it normal for the gas to go out and then come back on again as that is what is happening.
I have, in fact, called out the Engineer who serviced the boiler and he will be here next week but I like to try and understand things if I can myself.
Any help or comments would be appreciated.

Bold turned off - Mod 10

 

[Gasguru]

Please turn off the bold.

It may be coincidence the problems started with the visit but I would first check the pump is set to the highest speed (ie it hasn't been adjusted down). This is easy to do yourself.

The sensors and burner pressures must be checked.

There is a filter located in the base of the pump - this may be partially blocked resulting in poor central heating.

When running the hot water the burner flames should adjust down as the hot water temperature increases past the set temperature on the front control. However if the temperature can't be maintained even on the lowest burner rate it will then cycle on/off.

What you describe though sounds as though the secondary heat exchanger may be blocked.

 

[kilrail]

Apologies for the bold didn't preview first. The pump is on highest setting. I suspect as the boiler is probably 8 years old or more it is probably suffering from clogged heat exchangers as you suggested, as we are in a hard water area .
There is an identical brand new boiler for sale on ebay (never been fitted bought years ago) and I am tempted to buy it for spares. However, I will wait now for the engineer and will post here if he solves the problem.

I appreciate you taking the time to answer.

 

[Gasguru]

I'd grab that ebay boiler.

With your boiler at 8 years old the fan and pcb won't have long left. The expansion vessel on yours will be flat (they are very difficult to maintain), and the plastic bottom end won't last forever.

If the plate exchanger is blocked its very difficult to remove.

Apart from some silly design faults (the hot water glands leaking) they will still be more reliable than most boilers on the market today.

It is normally illegal to install a non-condensing boiler but there is no reason you can't swap 99% of the parts ie leave the old flue in the wall for now.

 

[zimmers]

if the secondry h/ex was blocked then it wouldnt be coming on and off would it?,wouldnt it go to overheat and need resetting ,not a gas valve proplem solenoid sticking or a flow switch?

 

[Gasguru]

The Compact 80/100e's (and SD SD30's) are a little odd with even slightly blocked plate exchangers. It all depends on the DHW temp. setting on the front panel. They can be perfectly happy and modulate up to a certain setting, above this they will cycle from full burner to off.

Problems with these boilers are compounded by the horrible Honey VK05 gas valves - there is no seperate mod coil. The safety solenoids are PW modulated making measurements difficult.

 

[bengasman]

If the boiler goes off and comes on again when hot water tap stays open but varies in temp, it is almost surely carp in the plate exchanger. Would be consistent with rads being cold at the bottom.
Either chemical flush and take the boiler to bits or powerflush with fx2. Make sure your boiler can handle it before you go this way.

 

[kilrail]

I can't believe it, the boiler on Ebay went for £275 , I had bid £100 max.
I appreciate all your input and I guess when you move house you often find problems with the heating. I know I left behind an 18 year old Myson with cast iron heat exchanger but it was still working OK.

If there is no cheap / simple fix I will look to have a new boiler installed but then there is all the hassle of which one etc. The people who did the plumbing when we had our single storey extension done, said they could install a Baxi Main for £1,000 and I will wait and see what the Heating Engineer suggests on Tuesday and get a price from him as well.
I suppose you guys all have your favourite boiler but I keep hearing that the modern boilers aren't designed to last, also hard water being an issue etc etc.

The other thing that puzzled me was the fact that the rads were coldish for a few months before I noticed a problem with the water (shower) and that seemed to happen overnight. One minute it was fine and then a lukewarm moving to cold and back to lukewarm shower.

Since there are obviously quite a few experts on this forum, I wonder if anybody has come across the issue of a shower which worked absolutely fine but the temperature range from cold to hot took place withing the blue band on the dial i.e. I never even needed to move the dial to No 1.

This was how the Mira Excel was when we moved in. Now, with the problem it is cold right at the start of the "blue" and then the same as described all the way along the dial, lukewarm to cold etc.

I spoke to the Mira Technical people and they said they had never heard of it before. They mentioned imbalance of hot/cold but I explained it was a combi instal and the switch on the back of the cartridge was set to high pressure system as it should be. They could offer no other suggestion so I thought if the boiler is sorted and the shower goes back to how it was, I'll be happy enough.

I just wondered if that was a sign that there was a problem with the boiler system at that early stage or a completely unrelated mystery issue!

Apologies for this long drawn out post.

 

[bengasman]

I suppose you guys all have your favourite boiler but I keep hearing that the modern boilers aren't designed to last, also hard water being an issue etc etc.

So if you do a cowboy job, installing an inferior boiler in half a day and it gives up in the second year, you say: I told you modern boilers did not last.

A good combi, with the additional parts cost over a grand, so installing a boiler for a thousand quid????

 

[kilrail]

Sorry Bengasman, I think there is a misunderstanding here. The Company who quoted £1,000 for a Baxi Main are reputable Plumbers / Corgi registered gas installers based in Ipswich and trading since 1972. I have no idea about which boilers are good or bad and I was rather hoping that maybe you or some of your colleagues would give me an idea.

I don't mess with boiler installation , I leave that to the qualified experienced guys.

 

[bengasman]

Two issues here. As I do not know your plumbers, I could not know if they are good or bad. My remark about cowboy work was not meant for them.
There are a lot of people out there who will do a poor job and then blame problems on the design of modern boilers.
If you read through the many posts on this subject, you will find some very competent installers that say it is better to have a cheap boiler installed and serviced properly than an expensive one that is flung on the wall and left to die. And I agree. I have found though, that it is more often than not that cheap boilers are poorly installed as well, a combination that usually leads to never ending problems.
Unfortunately, you do not ALWAYS get what you pay for. One of my clients had a cheap boiler fitted in a sloppy way, and they still charged him 3 grand for it.
The best advice I can give you on this subject: find a local plumber who comes highly recommended by people you know and put your fate in his hands.

 

[Agile]

You must realise that radiators which are cold at the bottom is a sign of advanced sludge in your system.

This is a very serious situation which must be addressed before it gets totally blocked.

It is the result of a serious fault!

Often power flushing done properly ( not by Zimmers who reads trhe paper instead of running around like a blue assed fly ) is the only feasible solution to your problem!

You might be able to take each rad off and flush it out with a hose pipe in the garden. Not very good for champagne colour carpets though!

Tony

 

[kilrail]

Well my heating engineer turned up today and couldn't quite figure out what was going on. He seemed to think (like some of you) that there was sludge in the system as the rads were cold at the bottom.
I pointed out that when our extension was built about a year ago the plumber opened the filter / Y strainer at the outlet near the boiler and cleaned it out and the heating was brill after that. He said did I want him to do it ( I could have done it myself easily as there are isolating valves on both sides) but he is the Engineer so I asked him to ahead. He checked temperature measurements after and there seemed to still be a problem.

He suggested a power flush at £375 which would need to be done anyway if I had a new Valiant boiler fitted for £2,500. I agreed to power flush as there was obviously crap in the system visible from cleaning the strainer.

However After he had gone the radiators started to heat up and in no time at all they were absolutely stonking hot, all of them. No cold spots anywhere.

Now the only problem is the DHW - I tried winter and summer setting in case the central heating was affecting the water take off but no difference. The same thing was happening all the time - On running hot water on full flow the gas fired up for 20 secs then off for 11, on for 17 off for 12, on for 14 off for 13. Obviously this explains the fluctuating temperature but now that the CH is working spot on, does it make it easier for one of you experts to diagnose. GasGuru seems to know the boiler and hopefully will have a comment.

 

[Agile]

I expect its quite simple!

The strainer is probably on upside down and in removing the gauze the dirt dropped down into the pipe and when it was run again that dirt passed into the plate hE and has partially blocked it.

Its amazing how so many people follow the arrows on the filter case rather than logic. Thye are designed for mounting on horizontal pipe with the filter element pointing downwards.

Tony

 

[kilrail]

Hi Tony

This one is installed on a vertical 22mm pipe at 45 deg pointing down. But I suspect the filter should have been checked regularly. Strangely, the engineer told me today that it not a normal part of boiler service and all they usually do is give it a "bit of a clean"
Do you think the power flush will sort it?

Regards Steve